Results of experiment showed that an admixture,mainly consisting of rotenoneand fenvalerate(4:1)gave strong contact,stomach poison and antifeedant effectand the inhibitory effect on the growth and development of Pieris rapae L.,and the co-toxicity coeffcients for contact and stomach poison were 342.2 and449.8 respectively.The admixture was used to spray in 30mg/L in pot and fieldtrials,and it gave the same control efficiency to Pieris rapae as 50mg/L offenvalerate giving and was more effective than that of 75 mg/L of rotenonegiving alon.