Abstract: Comprehensive studies have been conducted to investigate sedimentary environment of the Maokou Formation in Huopu section. Panxian, Guizhou province. The results of this study revealed that there are 8 microfacies in the Mnokouan of Huopu area, which represent respectively the sedimentations of low energy environment below the wave base, epeiric sea with normal salinity, beach with hi energy and lagoon with restricted circulation, etc. The assemblages and distribution pattern of the microfaeies in the Huopu section demonstrated that the Maokouan sedimentation is dominated by open platform facies in the most time, but the late Maokouml is characterized by a transitional facies from the open platform to restricted platform. A further analysis on the shoaling upward sequence has suggested that the major environmental features changed remarkably during the Maokouan period. In the early Maokouan, transgression reached its climax in this area and the sea level was relatively high. The bottom of the sea in this stage was characterized by low energy and low content of oxygen. Therefore, the fossil benthos was of low abundance. The middle Maokouan deposits are typical open platform sedimentation formed in shallow-medium depth. The marine environment in this stage was characterized by clean water with normal salinity, abundant nutrition and high abundance of organisms. In the late Maokouan, the sea water became shallower and circulation was restricted. High salinity and depletion of oxygen caused by diversification of algae further suggested deterioration of a series of factors in marine environment, which consequently lead to the significant decrease in abundance of marine organisms.