Abstract: At present, in safety production of vegetable, the large dosage of pesticide forced the fastness of plant diseases and insect, killed many natural enemies and polluted environment, meanwhile it also menaced the health of human. The efficacy of medical disinfector H2O2 prevented disease of vegetable had researched in protected ground in this paper. The results indicated that 0.6% H2O2 was effective to control powdery mildew of cucumber. The incidence of powdery mildew of cucumber drop to 24.54% after used it. Compared with 0.5% Triadimefon, Its efficacy reached 67.94%. In addition, the efficiency of H2O2 was correlated to the times of use. Based on the results of experiment, the paper suggested we should spray twice 0.6% H2O2 and then one time 0.5% Triadimefon to reduce the dosage of chemical and the pollution of environment. The research had provided a new kind of measure for the disease prevention of vegetable safety production in protected ground of north of China.