With biological treatment of purple clam, the water qualities in tiger prawn ponds can be improved. However, the treatment delayed the infection of white spot virus syndrome (WSVD) but could not completely inhibit the happening of the disease. The infection of WSDV in control pond (S4) was found at 95th day, and then mass mortality happened after 2 days later. The same diseases were found at 117th day in treatment ponds (S2 and S3), at when we decided to harvest at once. The results of ponds after harvesting were as follows: In S2, the mean of body weight was 13.17 g and the total gain was 433 kg. The survival rate was 60%; In S3, the mean of body weight was 14.11 g and the total gain was 218 kg. The survival rate in the pond was less than that in S2, only 26%. The infection of WSDV in S1 and S4 were found at the almost same time and caused mass mortality. Water qualities such as pH, DO, ammonia-N, and NO2-N in all shrimp ponds were examined. During the experiment, all of them were in an adequate range.