The real-time measuring of particle diameter and velocity of raindrop is the key for the statistical of raindrop spectrum parameters. In order to obtain real-time, continuous, reliable and accurate statistical raindrop sample data, the light array method based on high speed line array CCD is adopted for non-contact measurement of the speed and diameter of raindrop. Raindrop images cache unit is structured by FPGA, which stores two rows of continuous dynamic raindrop images. With using FPGA parallel computing ability, raindrop dynamic image connected domain detection and mark algorithm are achieved rapidly by FPGA, and then realizing the particle diameter and velocity detection. The experiments show that this method can automatically and continuously measure and record the number, size and terminal velocity of raindrop, and provide a reliable sample data for the raindrop spectrum parameters statistical.