Abstract: A rapid and effective method was developed for determination of kresoxim-methyl residue in cucumber.Field trials were designed to evaluate the dissipation and residue of kresoxim-methyl in cucumber at Guangzhou and Tianjin.The dietary exposure and risk assessment were also conducted by using the calculation of risk quotient(RQ).The samples were extracted by acetonitrile and detected by HPLC-MS/MS.The results showed good average recoveries of 91%-95% with relative standard deviations of 3.74%-9.99% at the spiked level of 0.01,0.05 and 0.5 mg/kg.The limit of detection(LOD) was 0.001 mg/kg and the limit of quantification(LOQ) was 0.01 mg/kg.The results were found that the half lives of kresoxim-methly in cucumber of Guangzhou and Tianjin were 1.5 and 2.1 days,respectively,and the terminal residue was 0.08-0.23 mg/kg 3 days after application,and lower than LOQ value 5 days after application,the RQ of kresoxim-methyl were far below 1.It predicted that it was safe for human being when using this pesticide to control powdery mildew on cucumber.