Abstract: Used five lactic acid bacteria which screened from the tofu acid whey to ferment tofu whey. The p H values of tofu whey were taken as the evaluating index. Some factors affecting the fermentation conditions of tofu whey such as single strains fermentation, mixed strains fermentation, fermentation temperature, inoculum size and proportion of mixture were discussed. On the basis of single factor experiment, the orthogonal experiment was designed. The results showed that the optimal conditions of acid whey fermentation were double strains fermentation, proportion of mixture 1:9 (No1 and No3) , 5% inoculum size, fermentation temperature42℃, fermentation time 24 h. The p H value of tofu acid whey was 3.56.