Multi-strain mixed fermentation can provide a relatively complete lignocellulosic enzyme system compared with single-strain fermentation. This study was firstly to screen strains which have a strong ability to hydrolyse rice straw (RS) enzymatically and enrich true protein (TP). Then, the conditions in the process of SSF, including the optimum inoculum size of mixed strains, inoculation ratio, and different inoculation time of N. crassa 14-8, were optimized. The experimental results showed that the highest TP content could be obtained by using N. crassa 14-8, C. utilis, and P. chrysosporium as mixed strains, and 5mM Mn2+ and 50mM veratryl alcohol were used as inducers of lignin peroxidase (LiP) to improve the efficiency of enzymatic hydrolysis. When N. crassa 14-8 was inoculated 1day later than P. chrysosporium, the total inoculum size was 10%, and the optimum ratio of N. crassa 14-8 to P. chrysosporium was 1:2, the maximum TP yield (8.89%) was obtained, with 123.37% of its increase rate. This work proposed a technique with potential application in large-scale feedstuff protein conversion.