其构成形式如下：一、肯定式的类型：1. be型（即：系动词原形be＋表语＋其它）.如： Be careful! Don't go too high. 当心!别爬得太高. Be quiet, everyone! 大家请安静!2. do型（即：行为动词＋宾语＋其它）.如： Come in, please!请进来! Please open your books! 请翻开书!3. let型（即：Let＋宾语＋动词原形＋其它）.如： Let me have a look.让我看一看吧. Let me help you.我来帮你吧.二、否定式的类型：祈使句的否定式多以do not（通常缩写为don't）引起,也可用never引起.1. be型（即：Don't＋be＋表语）.如： Don't be lazy! 不要懒惰! Never be late again. 千万不要再迟到了.2. do型（即：Don't＋行为动词原形＋其它）.如： Don't throw the ball like that.不要那样扔球. Don't worry. I'll soon be all right.\x0d你们不要担心,我很快就会好的. Never do it like that.千万不要那样做了.3. let型有两种否定形式： １）Let＋宾语＋not＋动词原形＋其它.如： Let him not go there.别让他去那儿. Let's not waste time.咱们不要浪费时间了. ２）Don't＋let＋宾语＋动词原形＋其它.如： Don't let her go there.别让她去那儿.