Statistical analysis and double ratio analysis between the radar echo and the rainfall parameters of single cumulus were conducted by use of the 8 years (1979～1986) randomized experiment data of 28 seeded clouds and 20 controlled clouds observed in Hunan province.The results show that the total precipitation,rainfall amount,rainfall intensity and rainfall duration of the seeded clouds increase by a factor of 17%,28%,24% and 7% than those of the controlled clouds respectively.It is not obvious that antiaircraft gun seeding affects on the cloud top height and the cumulus area as well,but it is obvious that the seeding perhaps increases the radar echo strength of cumulus and decreases the echo depth of the strong core in the randomized experiment.