Physical properties of cloud particles on the top of cloud were analyzed by NOAA/AVHRR channel 3(3.55～3.93μm) data. Radar and precipitation data were used to validate the analysis results. It was showed that clouds with smaller reflectivity at channel 3 and with bigger size were easy to rain. It was found that there was good corresponding relationship between small reflectivity at channel 3 and radar echo when cloud is a single layer. It was testified that the result of size analyzed from satellite was the same as that from radar data during precipitation.