Based on the principle that the reflectivity at a water (or ice) absorbing band primarily depends on cloud particle size, the comparison of effective particle radius of water cloud is made, retrieved from the data of channel 3 (3.7 μm) of FY 3A Visible and Infrared Radiometer (VIRR) and the data of channel 6 (1.64 μm) and channel 7 (2.13 μm) of FY 3A Medium Resolution Spectral Imager (MERSI) using SBDART radiation transfer mode. The results show that the effective particle radius can be quantitatively retrieved by any of the three channels of 1.64, 2.13 and 3.7 μm. The reflectivity of channel 1.64 and 2.13 μm is more sensitive to the larger particles while channel 3.7 μm shows better sensitivity when optical thickness is smaller. The retrieve product of effective particle radius of the three channels have better correlations with the effective particle radius products of MODIS.