In the Southwest Mandarin of Sichuan and Guizhou,gei(给)and gen(跟)have many similarities in the functions.Gen(跟)can be used not only as a comitative preposition,but also as a benefactive marker,a dative marker,and even as a giving-verb,which has the same function as gei(给)in Mandarin.The multifunctional evolution of semantics is the main reason for the overlap of the functions of gei(给)and gen(跟).Gei(给)has experienced the semantic evolution of"giving>be-nefactive>human direction>comitative","giving>benefactive>recipient(before verb)"and"giv-ing>recipient(after verb)",while gen(跟)has experienced the semantic evolution of"comitative>human direction>benefactive>recipient>giving".The use of the benefactive marker gen(跟)in Sichuan and Guizhou may have brought by the immigrants in Chinese history,which creates conditions for gen(跟)to evolve into a preposition that elicits the recipient.The giving-verb gen(跟)evolved from gen(跟)that elicits the recipient in the structure of"N+gen(跟)+O+VP".When N is both the given item and the deliverer,it activates the information in the sentence that expresses the giving-event whereas "gen(跟)+O+VP"can be reanalyzed as a serial-verb structure from the adverbial-head struc-ture,and gen(跟)gradually becomes a giving-verb by antigrammaticalization.