Objective： To establish a detecting method for mandipropamid residues in cucumber by UPLC-MS coupled with the positive ions mods of MRM. Methods： The cucumber samples were was extracted by ultrasonic acetonitrile and then were purified by dispersed solid phase extraction (QuEChERS). Cucumber solution diluted with ultrapure water, and filtered by 0.22 μm water phase. Then 0.1% formic acid water (A) and acetonitrile (B) were used as mobile phase for isocratic elution. Results： The results showed that a good linearity was obtained for the standard curve of the method, its correlation was high, R²=0.999 8. Its detection limit was 0.003 mg/kg, and its limit of quantification was 0.009 mg/kg. Meanwhile, its recovery rate was between 89.6%～96.0% at the three levels of 10, 50 and 100 mg/mL. Conclusion： The method is simple, sensitive and reproducible. This method is suitable for qualitative and quantitative analysis of mandipropamid in cucumber, and it is a suitable method for rapid determination of mandipropamid in cucumber.