In order to obtain the eigenvalues of rain particles. In this paper, the threshold processing method is adopted to segment raindrops and the background image. The complex raindrop figure is converted to a binary image of the real boundary. The raindrops centroid is marked by using the mean algorithm, and the raindrop shape model is established by using the long axis information of raindrops. Combined with the global thresholds of Otsu and the local threshold method, a method for detecting the characteristic values of raindrops by Ostu is proposed. Through the experiment, it is shown that the method can effectively extract the characteristic values of raindrops from the image data. The number of particles and the shape of raindrops are indispensable parameters to measure the intensity of rainfall.