Abstract: The schemes describing the moist physical process in the meso-scale model include the microphysical scheme and the cumulus parameterization scheme. The rainfall calculated in cumulus parameterization scheme is in subgrid scale and the rainfall calculated in the microphysical scheme calculates is in grid scale. With the improvement of the model resolution, the microphysical scheme has become more and more important in the meso-scale model. More detailed microphysical processes are described in the mixed-phase microphysical scheme, so that it can be used in many researches such as microphysical mechanism of precipitation, the interaction between cloud and radiation, lighting activity of cloud and so on. Therefore, it is very necessary and significant to study and improve the mixed-phase scheme of the meso-scale model. GRAPES (short form of Global/Regional Assimilation and PrEdiction System) is the new generation numerical model system in China. In order to improve the physical processes in GRAPES model, CAMS (Chinese Academy of Meteorological Sciences) complex microphysical scheme is coupled with the meso-scale regional GRAPES system.CAMS complex microphysical scheme is a double-moment mixed-phase scheme. There are 5 kinds of hydrometeors in this scheme which are cloud water, rain water, ice, snow and graupel. The scheme includes 11 prognostic cloud variables. They are the mass content (Q_v, Q_c, Q_r, Q_i, Q_s, Q_g) and number concentration (N_r, N_i, N_s, N_g) and the extent of cloud droplet spectrum. There are 31 microphysical processes in the scheme. Not only the mass content can be predicted but also number concentration of hydrometeors. In this study, new microphysical variables and a new microphysical option are added into GRAPES. A numerical experiment is conducted using the new model. The case simulated is a heavy rainfall happening in North China during August 15—17, 2005. The model is integrated for 48 h with 60 s time step. Three other microphysical schemes are selected to simulate the same case to make a comparison.They are Thompson scheme, WSM6 scheme and NCEPcloud5 scheme. The simulated results of distribution of rainfall and hydrometeors are analyzed. Results are shown as follows. The distribution of rain band simulated by CAMS is similar to the observation and the development of rain band simulated by CAMS is consistent with those of other three microphysical schemes.The center of heavy rainfall simulated needs to be improved.The comparison of the regional average hydrometeors made between CAMS scheme and other three microphysical schemes shows the similar general characteristics. CAMS scheme is able to simulate the hydrometeors in reasonable distribution and value. Due to the different microphysical process in different scheme, the values of hydrometeors of four microphysical schemes are different. Results reveal the good capacity of CAMS scheme in describing cloud and precipitation processes in GRAPES model. The new scheme should be tested through numerical experiments and fine model design in the future.