A method was established to separate and quantitative analysis of diafenthiuron·thiacloprid 40%SC by HPLC,using acetonitrile+water(volume ratio of 65∶35)as mobile phase,on stainless steel column and SPD-20A UV detector,at 240 nm.The results showed that the linear correlation coefficients of thiacloprid and diafenthiuron were 0.997 0 and 0.993 0,the relative standard deviations were 0.22%and 0.18%,and the average recoveries were 97.89%and 99.42%,respectively.The method was precise and accurate,it could be used for the determination of thiacloprid and diafenthiuron in compound products.