Abstract: From 2007 to 2011,an aerial spraying pesticide of Beauvefia bassiana was used to prevent against Dendrolimus puncyatus.The result showed that the population density of Dendrolimus puncyatus before control significantly decreased year by year from 2007 to 2009,and kept at a low level between 2010 to 2012,but had no significant difference last year; The ratio of harmed trees before control was consistent with the population density of Dendrolimus puncyatus.The result also proved that when pesticide Beauvefia bassiana was sprayed to prevent Dendrolimus puncyatus in serious hazardous and moderately hazardous forests,the control effect was embodied as decreased population density of Dendrolimus puncyatus and decreased ratio of harmed trees in first 2 years,and kept low level in last 3 years.Therefore,the preventive control effect was very effective.