In the integrated ethanol and methane fermentation process, the mixture of digestate and stillage was reused as process water for the ethanol fermentation, which could not only provide enough nitrogen sources for ethanol fermentation, but also reduce byproduct glycerol production and enhance ethanol yield.Ammonium acetate was detected as the main nitrogen source in the mixed water.Therefore, in this study, effects of ammonium acetate, ammonium sulfate and ammonium chloride on ethanol fermentation performance were compared to reveal the mechanism for effect of the integrated ethanol and methane fermentation process on ethanol fermentation.Results showed that compared with two other nitrogen sources used in ethanol fermentation, ammonium acetate using as nitrogen source could lead to the shortest fermentation time, the highest ethanol yield and the lowest glycerol production.This indicated that ammonium acetate was the main factor that provided nitrogen source and enhanced ethanol yield in the integrated ethanol and methane fermentation process.Further studies showed that the main reason for the positive effect of ammonium acetate as a nitrogen source on alcoholic fermentation was the presence of acetate in ammonium acetate.