A method of selecting contrast cloud automatically and analyzing the seeding effect according to radar echo parameters is brought forward, aiming at physical test of convective cloud precipitation enhancement. Based on the Doppler radar data products, the contrast cloud is selected automatically in all convective cells at the very time when seeding by comparing their beginning time, position and orientation with those of seeded cloud, and calculating the analog deviation of varying characteristics of echo parameters before seeding. Then, it is presented the variation of echo parameters of seeded cloud and comparison between echo parameters of seeded cloud and that of contrast cloud. In view of this method, a set of seeding effect analysis software of convective cloud rainfall enhancement with radar products has been designed and developed. The software has been used in the precipitation enhancement operation experiments in Hubei Province. The results show that this method can identify the contrast cloud in realtime, eliminate errors caused by manmade judging to some extent, and make the effect analysis on convective cloud rainfall enhancement more scientifically.