Abstract: The wheat flour, corn flour, glutinous rice flour and rice flour were chosen as natural growth- promoting factors.The yellow serofluid was used as a medium.The acid content and pH values was taken as the evaluating index.In order to develop a natural coagulant of tofu, an investigation for some factors affecting the natural fermentation conditions of yellow serofluid such as different natural growth- promoting factors, fermentation temperature, fermentation time, inoculum size and the additive amount of the best natural growth-promoting factor was conducted.On the basis of single factor experiment, the fermentation conditions were optimized by uniform design combined with second order polynomial regression analysis for acid content.The results showed that with the fermentation temperature 37℃, 3% ( v /v) vol inoculum, fermentation time 24h, flour 7.5% ( w /v) , initial pH 6.2, the acid content was 0.8301g /100mL.