Huaxi area of Guiyang was located in the transitional belt from shallow-water carbonate platform to deep-water basin during the Early–Middle Triassic, and each sedimentary systems tract has its own characteristics especially the carbonate breccia wedge of lowstand systems tract(LST). The field investigation indicates that there are four times of carbonate breccia wedge of LST, which reflect this area experienced at least four significant sea level changes in the Early –Middle Triassic. The migration of carbonate breccia wedge also reflects the shifting of the platform margin and the relative sea level changes. Among them, the Guli breccia  wedge extended the farest distance to the platform, which represents that the platform margin shifted to the platform for the farest distance. The Zhangjiawan breccia wedge represents the fast sea level falling in the Early Anisian. In addition, this paper reconstructed the evolution of cabonate platform margin based on the analyses of  the depositional characteristics of the breccia wedge and the geometric relationship of each lithostratigraphic unit: ramp platform margin→depositional platform margin→reef by-pass margin.