Abstract: In this experiment,the acid peanut milk by co-fermented by Streptococcus thermophilus and Lactobacillus rhamnosus was used as the study object. The optimum fermentation bacteria were determined by pH,acidity,viscosity and viable count,and the optimum conditions for the preparation of acid peanut milk were determined by single factor test and orthogonal test. The results showed that the fermentation performance of Lactobacillus rhamnose in peanut milk was better than that of Lactobacillus bulgaricus. For the effect of peanut milk,the optimum fermentation conditions were as follows:ST:LGG was 2:1,inoculation amount was 5 mL/100 mL,fermentation time was 4.5 h,sucrose amount was 6 g/100 mL. At this condition,pH was 4.36,acidity was 76 °T,viscosity was 1532 mPa·s,viable count was 3.62×10¹¹ CFU/mL,sensory scores was 90,protein content was 4.78 g/100 g,soluble solids was 9.5%. The color of this acid peanut milk was milky white,rich fragrance,moderate taste,uniform tissue state.