This paper mainly discusses two questions about language contact, first, what is the direction of language contact, and two, what is the change of linguistic typology caused by language contact, and they clearly have different directions. Words usually diffuse from the strong language to the weak one by borrowing, and the structures usually diffuse from the weak to the strong by interference. In consideration of the feature of language contact, we have proposed an inverse principle of lexicon-structure. According to our long-term research of language contact, both mother tongue interference and lexical borrowing can make the structures of the mother tongue and the target language isomorphic. Mother tongue interference can change language more easily, resulting in the disappearance of a large number of typological features.