Using the airborne observation data from two continuous flights on 26 and 27 October 2008, this paper analyzes the cloud microphysical characteristics and precipitation mechanisms of the observed cloud system to reveal the microphysical process of precipitation in Sichuan Basin. The results show that: (1) The observed cloud system is a deep mixed cloud system, with cold in the upper layer and warm in the lower layer. The cloud top is around -10℃, and the 0℃ layer is high. The warm layer is deep (around 3200 m), while the cold layer is correspondingly thin (around 1800 m). (2) From top to bottom in the supercooled layer, the size spectra of the large cloud particles and precipitation particles become remarkably wider. (3) In the warm layer, the precipitation particles become smaller and decreased. (4) The existence of ice nuclei and supercooled water initiates the cold cloud process. The latter coordinates with the warm cloud process in the warm layer, and then the ground precipitation achieves. However, supercooled water is not abundant, and the precipitation particles formed are not plentiful, as well as the liquid water content in the warm layer is small, thus, the ground precipitation is small.