Abstract: This paper aims to provide the theoretical departure for the integration and perfection of the semantic system of Transitivity by comparing the Transitivity theory advanced by Sydney Grammar and Cardiff Grammar to illuminate the development of the study of transitivity in the framework of Systemic Functional Grammar (SFG).The study shows that these two major theoretical models of Transitivity demonstrate some remarkable similarities and differences.Then the possible reasons for the differences are explored, arguing that the two models are complementary, particularly on syntactic studies.This article is concluded with some prospects for further study of Transitivity.