Two-stage complete mixing ferment process was used for developing carbon source with primary sludge. The effects of hydrolysis retention time (HRT) and sludge retention time (SRT) on the ferment system were studied. The results showed that the effective HRT was between 32 h and 36 h, and the effective SRT was between 4 d and 7 d. Under above conditions, the average effluent SCOD was in the range of 980 mg/L and 1180 mg/L, and supernatant MLSS was in the range of 50 mg/L and 80 mg/L. And then, the separation effect of the sludge thickener was clearly. Acidogenic bacteria and methanogenic bacteria could be separated effectively in the conditions.