历年四级考试中的“How I Overcome Difficulties in Learning English”、“My Ideal Job”以及图表作文的第一段都属于说明文的范畴，如，2002年6月的根据坐标图写题为“Students Use of Computers”的作文。
说明文必须按一定的顺序进行说明：时间顺序、空间顺序、逻辑顺序或认识顺序，选择具体的特点和细节来说明。
所以，说明文的思路要围绕说明顺序、事物的特点和细节展开。例如：
范文点评
A Famous Clock
When you visit London， one of the first things you will see is Big Ben， the famous clock which can be heard all over the world on the B.B.C. If the Houses of Parliament had not been burned down in 1834， the great clock would never have been erected. Big Ben takes its name from Sir Benjamin Hall who was responsible for the making of the clock when the new Houses of Parliament were being built. It is not only of immense size， but is extremely accurate as well. Officials from Greenwich Observatory have the clock checked twice a day. On the B.B.C. you can hear the clock when it is actually striking because microphones are connected to the clock tower. Big Ben has rarely gone wrong. Once， however， it failed to give the correct time. A painter who had been working on the tower hung a pot of paint on one of the hands and slowed it down！
「点评」这是《新概念英语》中的一篇经典说明文，介绍了世界著名的“大本钟”。文章开篇指明该钟位于英国伦敦，且全世界的人们通过BBC就能够听到钟声。接下来讲述了“大本钟”的由来，特点——不仅外型巨大，而且走时准确，在结尾处讲了“大本钟”的一个幽默的小插曲——油漆工把油漆桶挂在指针上，把钟弄慢了。细读这篇文章，我们不难发现，区区159个单词就把“大本钟”的光辉形象牢牢地刻在读者的脑海里，为什么？本文基于事实，分析了主题的来龙去脉，语言简洁又不失生动贴切，作者态度客观又充满幽默，使读者既“明白了事理”，又对事物有较完整明晰的了解认识，此乃说明文之真谛也。
以“Goals”为题打开一篇说明文的思路。
参考思路
1）目标的分类：（可根据时间顺序，空间顺序、逻辑顺序或认识顺序，任选一个进行分类和排列）
2）各个类别的特点和细节：
3）组织成文：
范文点评
Goals
Everyone has goals. Many people do not reach their goals for lack of planning. These three sets of goals should be developed： lifetime， intermediate and short term.
Lifetime goals should be written out. These goals should be clear and reasonable. For instance， the goal to win a research prize is clear and measurable. Other lifetime goals might include publishing a certain number of influential books or articles， earning a departmental chairmanship at a major university， successfully competing for a grant from the National Science Foundation or securing a consultantship with a big corporation.
Intermediate goals relate to outcomes during the next few years. For the beginning doctoral student， intermediate goals may include completion of course work and preparation of a doctoral research proposal. Like lifetime goals， these are measurable and clearly stated.
Short-term goals involve outcomes expected during the next 12 months. These goals are more performance oriented， and they help with achievement of intermediate goals. Examples of short-term goals are earning an A in a course， learning how to program a computer or performing an experiment.
「点评」本文介绍了人生的三种目标：终生的、长期的和短期的目标。在文中采用了说明文常用的方法：定义、举例、分类和比较等。
我们要了解并且要掌握的方法：
1. 定义法（definition）
定义法是用下定义的方式去揭示事物本质特征或概念内涵。它能使读者迅速抓住本质属性和基本特点。此法的句型：
① … is a/the … of … which/that …② … relate to/involve/refer to …
「例」
（1）Language is a system of arbitrary vocal symbols which is used for human communication. 语言是人类用来交际的任意性的语音符号体系。
（2）Intermediate goals relate to outcomes during the next few years.
（3）Short-term goals involve outcomes expected during the next 12 months.
2. 举例法（illustration）
举例法就是举出实际事例来说明事物的方法，是最常见，往往也是最有效的阐释模式。
专家提醒
举例时应挑选具体、典型且有能力表达清楚的例子，并注意按照一定的顺序编排。
请看上述范文第二段：“For instance”引出“lifetime goals”的实例，如，赢得研究奖金、出版有影响书或文章、获得大学的系主任职位、获得国家自然科学基金及大公司稳定的顾问职位。
3. 分类法（classification）
分类法就是把说明的对象，按一定的标准划分成不同类别分别加以说明的方法。如：上述范文介绍人生的三种目标，并按照时间的长短对终生目标、长期目标和短期目标做了分类说明。
4. 比较法（comparison）
比较法是用一个事物和与其有联系的其他事物加以对比的说明方法。目的是为了帮助读者准确地区分事物，通过对比达到对该事物的深刻认识。
如：上述范文对三种人生目标在时间上和实际操作上进行了比较，并阐明了彼此的联系。
（1）Lifetime goals should be written out.
（2）Like lifetime goals， these are measurable and clearly stated.
（3）These goals are more performance oriented， and they help with achievement of intermediate goals.
5. 数字法（statistics）
数字法是运用数据来表明事物的本质和特点，准确合理的数据使文章精确可信。
「例」
（1）Nearly half of all Americans over age 20 wear a bridge or denture，and more than 20 percent have complete upper and lower denture. By age 50， one out of every two persons has gum disease.
（2）And it seems sensible to wait. One quarter of all marriages between people under twenty-one end in divorce. In Britain in 1972， there were 124，248 divorces.
说明文的说明方法除上面介绍的常见的几种以外，还有诸如分项法、列举法、比喻法及引用法等，只有综合运用多种说明方法，才能多角度、多层次地全面、清晰、准确地展示客观事物的本来面貌。
1. 用定义法解释：
CET-4：
the Olympic Games：
a skeleton in the cupboard：
Hope Project：
qualifications：
2. 用举例法说明：
教育的重要性：
当前网络游戏的危害：
成功的方法：
健身的种种看法：
大学生学好英语的方法：
3. 用分类法说明：
社会实践的方面：
课外活动：
大学生谈恋爱的原因：
大学毕业生的分配情况：
食堂的伙食：
4. 用比较法说明：
留学的利弊：
兼职的好坏：
不同的减肥方法：
题海战术与素质教育：
5. 用数字法说明：
大学生的身体状况：
大学生的就业现状：
汽油价格上涨带来的影响：
手机的使用情况：
中国人住房状况：
借助说明文的构思方法，看看下列题目该如何写：
（1）The Layout of a Hospital
Direction： You are asked to write a composition about “The Layout Of a Hospital”。 Locate some important departments in the hospital based on the picture and information given below. Your compositions should be no less than 100 words.
1）the Emergency Department
2）the Out-patient Department
3）the Surgery Department
4）Dispensary/Pharmacy
5）Physician Department
6）the Eye， Ear， and Throat Department
7）the Dental Department
8）the Laboratory
9）the X-ray Department
10）the Administrative Building
11）the Ward
参考范文
Near the gate， on the west side of the road is the Emergency Department. Opposite the Emergency Department across the Main Road is the Out-patient Department. The building to the southwest of the lake is the Dispensary， which faces the Surgery Department lying on the other side of the road. Along the west wall， from south to north， stand three buildings： the Physician Department， the Eye， Ear， and Throat Department， and the Dental Department. The Laboratory is to the northwest of the round about， and beside the Laboratory， the X-ray Department is located on the same side of the road.
A winding road by the lake leads to the Ward. Near the end of the main road， the Administrative Building is situated on the east side. The hospital is nicely and conveniently laid out.