A machine translation method and system comprises the steps of (a) formalizing a non-formal source language in an interactive or automatic way and (b) transforming the formal source language into a formal or non-formal target language in an automatic way. It eliminates the language barrier between person and person and the language barrier between person and computer: A user translates his/her non-formal native language correctly and without lexical ambiguity into any non-formal foreign language which he/she knows nothing about; a user and a computer exchange information in his/her non-formal native language correctly and without lexical ambiguity. It can be used in network terminal equipment, Internet knowledge bases, knowledge reasoning search engines, expert systems and automatic programming. That formalization of a source language is the common foundation for transformation into various target languages makes it especially suitable for multilingual machine translation.