Abstract: This article, by using Systemic Functional Linguistic theories, discusses the grammatical status of "preposition + clause" structure in Chinese.Taking the clause introduced by the preposition as the start point, the study examines grammatical relationship between the clause and the following clause and reanalyzes the function of the preposition.The result shows that preposition can also function as conjunctives which combined the two clauses into a clause complex when taking a typological perspective, while taking a topological view, the cline between outer circumstantial elements and dependent clauses is embodied in the continuum from "preposition + norminal group" to "preposition + clause".