英语中的词性的变化规则是什么呢 比如说一个动词的名词形式等

Sorry to say taht in general, there is no specific rule about it.

However, some of the nouns have regular forms, like -tion, -ment, -ary, ... which are called suffix, and you can turn to some dictionaries.

The best way for you to learn this is to memorize a certain amount of words, then you yourself can summarize the so-called "rule".