In order to improve observing accuracy of precipitation, a new method of area rainfall estimation by using radar, raingauge, and particle laser-based optical measurement instrument is presented. Firstly, the relationship of Z-I based on raindrop size distribution observed by the particle laser-based optical measurement is established. Then in order to obtain optimal adjusting factor, the variational method is used to adjust the measured adjusting factor between radar echo and raingauge data. Finally, rainfall is calculated by using the optimal adjusting factor. This paper analyzes the precipitation process on May 15, 2007 in Liaoning Province. The result indicates that the actual rainfall spatial distribution can be reflected preferably and the observing accuracy of precipitation can be improved by using radar, raingauge, and particle laser-based optical measurement instrument.