In this paper,Streptococcus thermophilus,Lactobacillus bulgaricus and Lactobacillus plantarum subsp.plantarum were domesticated to adapt to the fermentation environment of 100% pure soybean milk.The optimal production conditions were selected by single-factor experiments and orthogonal experiment.Ratio of three kinds of bacteria was 1∶ 1∶ 1,inoculum amount was 5%,fermentation temperature was at 40 ℃ and fermentation time was 5 h.Under the above optimum conditions,the acidity of fermented soybean milk was 98.7° T,the viscosity was 3875mPa·s,and the total bacterial count was 5.63 × 108 CFU /g.The fermented soybean milk had good curd effect,no whey separation,no bean flavor.The milk was delicate,smooth and white.This research provide technical reference for the development of high quality soy yogurt.