This paper used dried cowpea as materials to study the different proportion of water which effected the quality of cowpea with wild fermentation method. The results showed that, during the fermentation process, with the addition of water, the cowpea’s pH value decreased. The total acid content increased with the water addition except when the amount of water was 12%. The peak of nitrite was slower and lower than others when proportion of water was 16% and 20%. The content of volatile ester increased firstly, then keep invariability. And the content of volatile ester was higher than the proportion of water was 14%,16% and 18%. After 32 days, the amino acid contents which the water addition was 16% higher than other treatments; with the increased of water content, the cowpea’s hardness, adhesive and chewiness were decreased at first, then increased. Taken together, when the proportion of water was between 14%~16%, the quality of cowpea with wild fermentation method was the best.