Abstract: Based on a synthetic study of sedimentary facies,logging facies and seismic facies,Shaximiao formation in Zhongjiang area,Sichuan province was considered to be deposited in a fluvial-lacustrine environment.It underwent evolution process of shallw lake,semi-deep lake,sublacustrine fan,delta to meande ring stream environments from early to late periods.The favourable zone for gas accumulation was pointed out according to the characteristics of sedimentary microfacies in different periods and their distribution.