Part or GMS infrared,visible digital cloud maps and synchronous measurements of rainfall during the 1991 Meiyu wet period are used to investigate the relations of tainfallintensity to the brightness on the IR and visible maps by examining the 2D frequency ofclouds producing precitation of different categories, and based on these relations obtainedthe precipitating clouds(for heavy raingush,rainstorm,hard rain and moderate-light rainfall)are identified in terms of the bi-spectral(IR and visible)thresholds, with total accuracyreaching 73.4% and the acctiracy higher in the case of weak precipitation clouds than ofstrong ones.