Abstract: Based on the BCC_RAD (Beijing Climate Center radiative transfer model) and a multi-shape ice cloud radiative parameterization scheme, the effects of different ice crystal weight assumptions on ice cloud optical properties and radiation are discussed in detail. The results show that the influences of the ice crystal weight assumption chosen on the ice cloud longwave band-averaged volume extinction coefficient, the single scatter albedo and the asymmetry factor are obvious. The ice crystal weight assumption has a significant influence on longwave radiative flux. For the longwave downward radiative flux, the assumption can cause up to 10.50 W/m² of the flux difference at the cloud base. For the shortwave upward radiative flux, the assumption can cause up to 15.05 W/m² of the flux difference at the cloud top. The ice crystal weight assumption also has a significant influence on the shortwave radiative flux. For the shortwave downward radiative flux, the assumption can cause up to 12.48 W/m² of the flux difference at the cloud base. For the shortwave upward radiative flux, the assumption can cause up to 10.23 W/m² of the flux difference at the cloud top. The assumption also has a great effect on longwave heating rate, which could be 1.31 K/d at the cloud top and -2.06 K/d at the cloud base. In summary, the weight assumption has an important influence on ice cloud optical properties and radiation calculations, particularly in the longwave region.