Abstract: In order to improve conversion rate of acetic acid and methane yield in anaerobic digestion, an atificial composite system Th3 was constructed by mixing three strains of acetogenic bacteria CD-2 (Clostridium sordellii), ZY-3(Clostridium bifermentans) and ZQ-1 (Clostridium butyricum). The experimental results showed that the optimum fermentation conditions of Th3 were as follows：initial pH was 7.0-8.0, sequence of three bacteria inoculation was ZQ-1, ZY-3 and CD-2, inoculation ratio was 1:2:1, and inoculum was 6% of effective volume. At the same time, the acetic acid yield was observed as high as 0.65 g/(L·d) at 30°C with static culture. The metabolic process of Th3 was proved to be very stable within ten generations. At(26±1)°C, the daily biogas production and productivity were improved significantly after Th3 addition in the initial and medium fermentation, and the start-up phase was shortened by 2-3 days. But the biogas process had no significant change when Th3 was added at the late stage of fermentation. The research can provide a reference for the complex strains construction, anaerobic digestion efficiency improvement and optimization of fermentation process and has an application value in biogas production.