In order to explore the prevention and cure function of microbial source fungicide to cucumber pow-dery mildew, chemicals and water treatment were used as control, a preparation of chitinase microbial sources asmain component was made to prevent and control cucumber powdery mildew. Incidence of powdery mildew of cu-cumber, root activity, and a series of biological properties and quality were determined. Through a microscope, itwas found that the preparation could inhibit fungus reproduction by destruction of powdery mildew pathogen sporescell walls. The plant test showed that incidence of powdery mildew was 8.77% in microbial preparation treatment.The control effect was 89.32%, which was far higher than controls. The yield increased by 15.7%. Quality indexsuch as total amino acid content and root vigor were significantly higher than the control. The research showed thatthe preparation could effectively reduce the incidence of powdery mildew of cucumber and promote plant growth atthe same time. The preparation has potential application value.