Based on core observation, thin section analysis, logging and seismic data analysis, we studied the rock types, sedimentary characteristics and reef flat distribution of the Upper Ordovician Lianglitage Formation in Halahatang area. The result shows that during the depositional stage of Lianglitage Formation, the sediments are mainly of nodular limestones and lamellar calcarenites, and the depositional environment is marginal facies in carbonate platform. In the plane, it successively developed basin facies, platform foreslope, reef flat on the edge of platform and platform margin depression from south to north. The reef flat on the edge of platform is distributed in the direction of EW, with great thickness and fine lateral continuity. The calcarenites of reef flat facies on the edge of platform can act as the favorable reservoir.