说明文的写作方法有好几种，如：分类法、解释法、举例法、定义法、比较法和因果法等等，现以前三种为例加以说明。
A.分类法
分类法就是按一定的标准把要说明的对象分成若干类，分别加以说明。
分类法的写作步骤：
段首句点明主题→分别列举内容→得出合理的结论。
分类法的写作要领：
①被说明的对象必须是同属不同类或同类不同种的事物，不同属、不同类的事物不能用分类法。
②分类标准必须统一，不可中途变更标准。
分类法常用的关键词：
firstly, secondly, finally (lastly), kind, sort, variety, include, involve, exclude, class, classify, contain, likewise, in addition, furthermore, besides, conclusion...
请看下面一则短文：
Typewriters
Whether you work at home or run a small business, or do personal correspondence, the latest development in office equipments will prove useful and convenient. With so many different typewriters to choose from these days, you can easily find a proper one.
The basic form of typewriter is the manual typewriter. Most of them are lightweight machines with few moving parts to go wrong, and they are reasonably inexpensive. Perfectly adequate for most household purposes, manual typewriters are especially useful for students and beginners.
Unlike manual machines, an electric typewriter has an electric motor. This means you can get characters regardless of the pressure with which you strike the keys. These machines are more convenient than the manual ones.
The most advanced typewriter, the multi-printer, is hardly recognized as a typewriter. It is a lightweight, silently operating machine which produces high quality printing by means of small dots. It is a highly adaptable machine with the capacity for many functions besides that of simple typing. This, together with its reliability, can make it extremely useful in the business situation.
However, in choosing a typewriter, first, the machine should meet your needs, and second, you should pay more attention to which one best suits you.
分析：
本文在第一段点明主题：在很多种打字机中选择适合自己的一种是很重要的，在接下来的三段里，分别说明了手动打字机(the manual typewriter )、电动打字机(the electric typewriter)和多功能打字机(the multi-printer)的性能和特点。最后一段得出结论：根据自己的实际需要选择合适的打字机。整个文章的思路明确、条理清晰。
B.解释法
简单地说，解释法就是说明"如何做某事，某事物如何工作"的一种说明方法。
解释法的写作步骤：过程第一步→第二步→第三步……
解释法的写作要领：在写作的过程中，应按照解释说明的顺序，一环扣一环地安排资料，不要节外生枝，插入其它细节，以保持整个过程的连贯性。
解释法常用的关键词：
①The first step→the second step→the third step→finally...
②To begin with→then→finally...
③Start→until→then→finally...
请看下面的短文：
Making Bread
There are four separate stages in making bread. The first stage begins by mixing yeast(酵母) with warm water. This mixture is then added to half the amount of the prepared flour. The resultant batter(面团) mixture is then left for an hour. At the next stage the rest of the flour is added to the risen batter mixture, along with sugar and oil. The main step in the second stage is a thorough kneading(揉成团) of the dough, after which it is left to rise. The third stage involves shaping the dough into loaves; the shaped loaves are then put into bread tins. In the final stage the bread is baked in a hot oven. The whole process of bread-making finishes when the bread is taken from the oven and left to cool on racks.
从这则短文中，可以看出"制作面包"的整个过程：第一步是用酵母和好面，第二步在"发了的面"(the risen batter mixture)里加进面粉、糖和油，然后揉成团，让它再次"发"起来，第三步把面团做成面包状，然后放进面包烤模(bread tin)里，最后一步是把它们放在烤箱内加热，然后拿出来放到架子上，使它们变凉。整个过程清楚明了，即使从来也没有做过面包的人也可以动手试一试了。
C.举例法
举例法就是用举例的方式来说明复杂的事物,这类作文的题目往往是：怎样理解……,为什么说……,试举例说明……,其要说明的内容往往是社会生活中人们对某些事物或现象的看法。
举例法的写作步骤：
给出主题句→用举例的方式来说明→结尾重述主题。
举例法常用关键词：
for example, for instance, such as, namely, that is to say, frequently, especially, in general, in particular, to illustrate...
请看短文：
The Older, the Weaker Mind?
Many of us believe that a person's mind becomes less active as he grows older. But this is not true, according to Dr. Jarvik, professor of Psychiatry at the University of California. She has studied the mental functions of aging persons for several years. For example, one of her studies concerned 136 pairs of identical twins, who were first examined when they were already 60 years old. As Dr. Jarvik continued the study of the twins into their 70s and 80s, their minds did not generally decline as people thought.
However, there was some decline in their psycho-motor speed. This means that it takes them longer to accomplish mental tasks than it used to. But when speed was not considered to be a factor, they lost very little intellectual ability over the years. In general, Dr. Jarvik's studies have shown that there was no decline in knowledge or power of reasoning. This is true not only with those in their 30s and 40s, but with those in their 60s and 70s.
It is true that older people themselves often complain that their memory is not as good as it once was. However, much of what we call "loss of memory" is not that at all. For example, the older person perhaps had trouble in hearing and seeing, or was trying to learn the new thing at a fast pace. Although their mind seems to decline, it is not necessarily a sign of decline due to old age. Often it is simply a sign of a depressed emotional state.
分析：
第一段引出话题：人的脑力与年龄无关，第二段利用博士的研究实例进行了说明，最后一段得出结论：脑力的变化与年龄无关，完全是人的情感影响所至。
