一、动词不定式在句子中不能充当谓语，没有人称和数的'变化。

　　二、动词不定式是由“to+动词原形”构成(有时可以不带to)。动词不定式的否定形式是“not+动词不定式”(not不与助动词连用)。

　　三、动词不定式短语具有名词、形容词和副词等的功能，可在句中用做多种句子成分。

　　1、主语：常置于句末，而用it代替其做形式主语。

例：

　　To go in for sports helps you stay fit.

　　It helps you stay fit to go in for sports. It is dangerous to swim in the deep sea on your own.

It's right of him to refuse the invitation1.(him为逻辑主语)

　　2、表语：Our duty is to protect the enviroment.

　　3、动词宾语：此种情况可按固定搭配或句式去记。

　　例：would you like to see my photos?

　　Kevin planned to visit his uncle.

　　I found it very difficult to get a job.(it为形式宾语)

　　4、宾语补足语：

　　(1)在多数复合宾语及物动词后要带to。

例：I asked a friend to read it to me.

　　(2)在表示感觉、致使等意义的动词(see，watch，hear，feel，notice，observe，make，let，have，help等)后不带to。

　　例：They heard him sing a pop song in the meeting room.

　　5、定语：动词不定式做定语放在所修饰的名词的后面。

　　例：Vinny is the first disabled2 person to sail3 around the world.

　　6、形容词补足语：在表示心理、感情、评价等的形容词后，对其进行补充说明。

　　例：Weareverygladtomeetyouagain.

　　7、状语：表示目的、原因、程度等。

　　例：They brought in photos of their families for me to look at.