[Aim] The safety of 66.5% propamocarb hydrochloride aqueous solutions (AS) in cucumber was evaluated, and the residual content of the pesticide on cucumber was studied, providing a scientific basis for the rational use of this pesticide.[Method] A 108.6 g·hm^-2 dose of propamocarb was sprayed twice on cucumber crops, with a 7 day interval between each application. Samples were collected after the last pesticide application. The concentrations of propamocarb hydrochloride residue were detected using liquid chromatography-tandem mass spectrometry (LC-MS/MS).[Result] When the concentration of 66.5% propamocarb hydrochloride AS was 0.05, 0.15, 1.50, and 5.00 mg·kg^-1 in the cucumber, the average recovery of the propamocarb hydrochloride was 72%-107%, with a relative standard deviation (RSD) ranging from 1.7% to 3.2%. Degradation dynamics of propamocarb hydrochloride residue in Changsha, Nanning, and Hangzhou in cucumber were followed the first-order kinetic equation C_t=C₀e^-kt. The half-life (T_1/2) of propamocarb hydrochloride AS on cucumbers was 1.1-4.9 d, which was a easily degradable pesticide (T_1/2<30 d).[Conclusion] According to the research results in 12 places, we suggest that the optimal dosage of 66.5% propamocarb hydrochloride AS applied on cucumber is 108.6 g·hm^-2, and the interval period between two applications should be 7 days. When harvesting, the concentrations of residual propamocarb hydrochloride would thus meet the residual standard requirements.