Aiming at the problem that the current flow standard instrument used to test the tipping bucket gauge or using glass ball with similar rain drop property is not possible to detect the optical raindrop spectrometer, we design a detection device for raindrop spectrometer based on STM32, which processes data and control system, adjusts the velocity of particles by controlling the speed of the disk, and pastes the discs with different diameters on the disc to simulate the particle size. And it is used to test the optical raindrop spectrometer whether can judge precipitation particle velocity and scale. The experiments show that the falling velocity and size of the simulated precipitation can be controlled at the same time, and the design has important practical value to test and measure the accuracy and performance of the raindrop spectrometer.