A detailed analysis of macro/micro structure for stratiform cloud in a high-pressure system rear over mountain has been conducted on data including airborne DMT(Droplet Measurement Technologies), radar, and weather chart etc. obtained from field campaign on 18 August 2010 in Beijing, and the precipitation formation mechanism is preliminarily discussed. The results show that the stratiform clouds in case consist of two layers, with the top layer the cold clouds and the bottom one the warm clouds. The aggregates of ice particles are found to widely and randomly spread in the whole cold layer, where the ice particle shapes are mainly plate, supplemented by column and graupel. Furthermore, the precipitation results from the seeder-feeder mechanism in which low level supercooled clouds are seeded with ice crystals from above. In addition, both aggregation and riming (accretion of liquid water) growth of ice crystals are also observed in the cold clouds, and the riming mainly occurs close to melting layer in the lower-middle part of the cold layer.