A plant oil bio-fungicide（SOL） was used in the prevention and treatment of cucumber powdery mildew.The study was to screen out the optimal concentration for preventing and controlling of cucumber powdery mildew.The control effect of SOL at 300 times was very significantly better than other concentrations, which preventive effi-cacy of the potted experiment was 100%, the therapeutic efficacy was 97.54%. The therapeutic efficacy of earlystage disease in greenhouse experiment was 86.09%, and at the mid disease stage, it was 60.84%. The control effectof SOL at 300 times was significantly higher than thiophanate methyl. The results suggested 300 times of SOL hadvery good control effect on cucumber powdery mildew.