Abstract: After the larva of Dendrolimus spectabilis Butler was infected by Cytoplasmic polyhedrosis Virus (CPV), the mortality of larva decreased with increase of infection period, increased with the increase of the dosage of treatment.The mortality of late-maturing larva was low after infection, but after the larva changed into pupa, the mortality was as high as 53.3% while the eclosion ratio was about 25.1%~27.5%.The amount of oviposit of adult decreased 40.9%than those of uninfected ones, some of the adult even did not lay eggs.The hatching ratio decreased 10~20 percentage the normal, while the ratio of filial larva carrying virus was as high as 61.1% and the mortality was 49.8%.Applying CPV and Bt together could decrease rapidly the eating amount of larva and increase the effect of insecticide.Compared with using CPV alone, the excreta amount of larva was about 1/2~2/3 five days after treatment.The value of LT50 differed at most 3.6 days and LT90 differed at most 6.9 days.