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：Becareful!Don'tgotoohigh.当心!别爬得太高.Bequiet,everyone!大家请安静!2.do型（即：行为动词＋宾语＋其它）.如：Comein,please!请进来!Pleaseopenyourbooks!请翻开书!3.let型（即：Let＋宾语＋动词原形＋其它）.如：Letmehavealook.让我看一看吧.Letmehelpyou.我来帮你吧.二、否定式的类型：祈使句的否定式多以donot（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'tbelazy!不要懒惰!Neverbelateagain.千万不要再迟到了.2.do型（即：Don't＋行为动词原形＋其它）.如：Don'tthrowtheballlikethat.不要那样扔球.Don'tworry.I'llsoonbeallright.x0d你们不要担心,我很快就会好的.Neverdoitlikethat.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：Lethimnotgothere.别让他去那儿.Let'snotwastetime.咱们不要浪费时间了.２）Don't＋let＋宾语＋动词原形＋其它.如：Don'tlethergothere.别让她去那儿.