In order to prepare the compound microbial agent for distiller’s grains to produce bio-organic fertilizer，the compound effect of mutation breeding strain UN-5 and Trichoderma reesei was investigated. Single factor and orthogonal experiments were designed according to the main factors such as acid resistance，antagonistic resistance，culture time， strain ratio and pH. The results showed that the ratio of bacteria，culture time and pH had significant influence on the cellulase activity. The results of orthogonal experiment showed that the optimal conditions for the preparation of the composite microbial agent were as follows:the culture time was 28 h，the strain ratio(UN-5∶Trichoderma reesei)was 2.5∶1，and the culture pH was 5.0. Under these conditions，the cellulase activity was 125.24 U and the effective viable number was 10.3 billion per gram.