Ice crystal multiplication is added into rain category model developed by Guo Xueliang et al.〖KG-*6〗,the influences of multiplication on microphysical structure of stratiform clouds are studied.Results indicated that,multiplication occurred at 190 min,ice crystal concentration increased to 7.3 L-1 from 10-3 L-1,then decreased rapidly and became close to the condition without multiplication at 250 min,the maximum rain intensity increased and amounted to 1.8 mm·h-1（6.6%）; during the 60 minutes after multiplication starting,cloud water content below multiplication layer decreased about to 0.05~0.2 g·m-3; ice water content increased to 0.1~0.6 g·m -3 at 190~230 min and then decreased to 0.1~0.3 g·m-3 at 240~250 min and nearly the same as the condition without multiplication after 250min; vapour content decreased to 0.1~1g·m-3 rapidly within 2400~4800 m altitude .The conclusion can be made as follows: (1) cloud water and vapour content decreases after multiplication process; (2) ice water content increases first and decreases later with the process; (3) 〖JP2〗multiplication increased the instantaneous ice crystal concentration and the maximum rain intensity.