A composite sounding flight was made during a shearline precipitation process in Jilin Province on 1 July 2004. The microphysical structure, precipitation mechanisms of this precipitation process are analyzed by means of the airborne Particle Measuring System (PMS) data, and the microphysical structure characteristics of the shearline precipitation cloud system and the physical mechanisms of rainfall formation are analyzed compositely. The results show that this shearline rainfall clouds mainly consist of altostratus, nimbostratus, and fractus; the average cloud droplet concentration and average cloud droplet diameter are different in three kinds of clouds; the cloud water content is distributed unevenly with increasing height; and the different parts of the clouds have different cloud water contents. The precipitation cloud system measured by PMS conforms to the concept of Bergeron seederfeeder cloud mechanism. The comprehensive analysis of cloud pictures and other sounding data shows that ice crystals mainly appeared in the upper part of altostratus or resulted from the spreading of ice crystals in cirrostratus, and feeder clouds are the central and lower parts of altostratus and nimbostratus.