This research is to examine the meaning and syntactic character of “gao” and to establish the verbal category of “gao”. “gao” is able to adopt both nominal and verbal objects. When “gao” adopt nominal objects, its meanings expanded into various detailed meanings, as significations of “work in”, or “engage in” gradually disappeared with the effect of generalization and harmony principles of the grammaticalization mechanism. Expansion in meanings of “gao” was possible since emptying of meaning was accompanied by the process of grammaticalization. This is due to the fact when realizing grammatical functions that substitute something in the world of discourse shared by narrators and listeners, it is in general easy to utilize morphemes that contain almost no meaning. That is, “gao” became to possess the function of a pro-verb through the grammaticalization process. Meanwhile, it is not irrelevant with the historical backdrop that “gao”, containing the meaning of “engage in”, was combined with two-syllabled verbs. Verbs that conjoined with “gao” at the time were in most cases borrowed from Japanese or were newly-coined two-syllabled noun-verbs made by China. Consequentially, it became to take the form that resembles the structure of dummy verb. Nevertheless, “gao” cannot be considered as a dummy verb in that it simply takes a morphologically similar two-syllabled noun-verb, and does not correspond to the syntactic and pragmatic functions of dummy verb. Therefore, “gao” can be considered as a pro-verb when it takes both nominal and verbal objects, since it is introduced whenever it substitutes the meaning of a verb or when the narrator intentionally attempts to express ambiguously. This can be said to be the outcome of grammaticalization.