Abstract: In this paper, a reservoir system is proposed based on the characteristics of the tight clastic rocks in the western Sichuan Basin. Such a reservoir system is defined as a geological body with effective pores and permeable channels of three-dimentional space,but without limitation on lithology and formational boundary. It is an important reservoir pattern for gas accumulation in tight clastic rocks. With combination of the geological settings of the west Sichuan Depression, the authors discuss the identification and the formative conditions of the reservoir systems in the paper.