Abstract: In this paper culture medium and fermentation process of function bacteria was optimized to improve the living bacterium content for compound microbial fertilizers, and in the purpose of contribution to the basis for the mass production of compound microbial fertilizer. The experiments with one factor and orthogonal design were conducted to optimize culture medium and fermentation process of nitrogen-fixing bacteria, phosphate-solubilizing bacteria and potassium-solubilizing bacteria for compound microbial fertilizers. The results showed that (1) the optimal medium for nitrogen-fixing bacteria was 7.5 g maltose, 15 g peptone, 0.03 g NaH₂PO₄·H₂O, 0.5 g K₂HPO₄, 0.2 g MnSO₄·2H₂O, 0.2 g FeCl₃ and 0.5 g MgSO₄·7H₂O, and the optimal culture condition included initial medium pH of 6.4 with inoculum size of 100 mL, rotation speed of 180 r·min^-1, and the optimal fermentation condition was 30℃.(2) the optimal medium for phosphate-solubilizing bacteria was 7.5 g maltose, 15 g peptone, 0.03 g NaH₂PO₄·H₂O, 0.5 g K₂HPO₄, 0.2 g MnSO₄·2H₂O, 0.5 g FeCl₃, 0.5 g MgSO₄·7H₂O,and the optimal culture condition included initial medium pH of 6.8 with inoculum size of 300 mL, rotation speed of 180 r·min^-1, and the optimal fermentation condition was 30℃.(3) the optimal medium for potassium-solubilizing bacteria was 7.5 g mannitol, 15 g beef extract, 0.03 g NaH₂PO₄·H₂O, 0.5 g K₂HPO₄, 0.2 g MnSO₄·2H₂O, 0.5 g FeCl₃, 0.5 g MgSO₄·7H₂O,and the optimal culture condition included initial medium pH of 7.6 with inoculum size of 100 mL, rotation speed of 180 r·min^-1, and the optimal fermentation condition was 34℃.