This study was conducted to investigate the effects of soy protein and pea protein on fermentation characteristics and microbial protein synthesis ability by in vitro fermentation. Fecal extract of health adult was used in vitro fermentation， the degree of hydrolysis （DH）， pH values， and the concentrations of ammonia nitrogen （NH3-N）， microbial crude protein （MCP）， volatile fatty acid （VFA）， including short chain fatty acid （SCFA） and branched chain fatty acid（BCFA） were determined， in vitro technology were used to study casein， soybean protein and pea protein impacts on these indexs from broth in vitro fermentation in different culture time（0 h， 24 h， 48 h）. The results indicated as follows： （1） The degree of hydrolysis of soybean protein and and casein group were significantly higher than the pea protein group. （2） At 24 h fermentation， the pH value of protein substrate addition group were lower than that of the control group， and soybean protein group was the lowest. （3） At each time point， the concentrations of NH3-N and MCP of protein substrates addition group were significantly higher than control group， the soybean protein was the highest， and pea protein was next. （4） With increased the fermentation time， the concentrations of SCFA and BAFA were also increased， and the concentrations of SCFA of soybean protein was significantly higher than that of pea protein group and casein group， and the concentrations of BCFA of soy protein and pea protein group were significantly higher than that of casein group. Therefore， soybean protein and pea protein are added to food which is beneficial to the synthesis of MCP and the production of VFA in intestinal microflora， and it is good for gut health.