We studied the effects of foliar spraying silicon (500, 1 000, 2 000, and 4 000 mg/L) on growth and development, antioxidant enzyme activity, yield and quality in Astragalus membranaceus var. mongholicus during seedling stage, flowering stage and rhizome elongation stage by randomized trial group, and also detected the control effect of foliar spraying silicon on powdery mildew and root rot to reveal the mechanism of silicon on enhancing disease resistance, improving quality and yield of A. membranaceus var. mongholicus, and provide theoretical basis for efficient cultivation of A. membranaceus var. mongholicus in production. The results showed that: (1) the application of different concentrations of silicon could increase plant height, stem diameter, plant width and chlorophyll content, and promote the growth of A. membranaceus var. mongholicus, and better treated with 2 000 mg/L silicon concentration. (2) Spraying silicon with different concentrations could increase the activities of antioxidant enzymes such as SOD, CAT, POD and APX and reduce the content of MDA in different growth stages. It was better at 2 000 mg/L silicon concentration during flowering and rhizome elongation. (3) When the silicon concentration was 2 000 mg/L, the control effects of A. membranaceus var. mongholicus against powdery mildew and root rot reached the highest, 47.22% and 38.80% respectively. (4) Spraying silicon with different concentrations could increase the dry and fresh biomass, yield, soluble extract and astragaloside IV content of single plant of A. membranaceus var. mongholicus, When the concentration of silicon was 2 000 mg/L, the contents of soluble extract and astragaloside IV increased by 16.48% and 31.96% respectively. It was found that foliar spraying of appropriate concentration of silicon could significantly enhance the resistance to powdery mildew and root rot of A. membranaceus var. mongholicus, promote plant growth, significantly improve the yield and quality of medicinal materials, and the effect was the best when the silicon concentration was 2 000 mg/L.