Machine translation is essentially a simulation of human thinking and language activities. Its paradigm can be seen in the followlling diagram.

There are two main systems for machine translation：

1、rule-based system

The rules of rule-based machine translation system can be divided into three types：

1)直接翻译,即只采用简单词法规则进行双语词汇层次上的对应翻译。

2)结构转换翻译，指同时应用词法和句法规则进行双语结构转换。

3)中间语翻译，即人工设计出一种本身不存在歧义的中间语，它与所有自然语言相对应，任何两种语言都可以通过这种中间语来寻求对应，获得翻译理解。

2、corpus-based system

The corpus-based machine translation system can be subdivided into:

1) statistics-based

2) example-based