Abstract: Abstract: Corn stalk has a compact structure and strong anti decomposing ability. Under natural conditions, it often takes a long time to be decomposed. Therefore, it has become a hot spot at home and abroad to accelerate the decomposition of corn stalk and make it harmless and resourceful. Comprehensive comparison of various technologies, using microorganisms to produce cellulase to decompose and transform cellulose, is considered as an effective way for cellulose utilization. To produce biogas by anaerobic fermentation, corn stalk must be pretreated to solve the problem of hydrolysis and acidification. In this study, a reasonable microbiological pretreatment method was used for anaerobic digestion of corn stalks. The complex microbial flora HK-4 is composed of Aspergillus, Trichoderma, Penicillium and white rot fungi. The effects of HK-4 on the pretreatment and anaerobic digestion of corn stalks were studied. The mixed ratio of 4 species of bacteria was 1:1:1:1, and the number of spores per fungus was 108 CFU/mL. The compound microbial flora HK-4 was added to corn stalk with a diameter of 0.7 to 1 cm, and cultured at 28 ℃ with a shaking rate of 190 r/min. The growth of the complex strain HK-4 could be divided into 3 stages: rapid increase phase, stabilization phase and reduction phase. The pH value of the compound bacteria strain showed a tendency to decrease at first and then increase. After 13 d operation, the value of pH was about 8.1. During the whole microbial pretreatment process, the value of pH fluctuated between 6.79 and 8.28, indicating that the compound strain HK-4 had good self-regulation ability and could maintain the stability of pH value. The solute chemical oxygen demand showed a stable situation overall, and the change of wave was reciprocating. The degradation rates of cellulose, hemicellulose and lignin were 64.52%, 51.06% and 3.89%, respectively. Using HK-4 treated corn stalks for biogas producing, the compound microbial strain group produced 7 364 mL biogas, which was 27.4% higher than that in the untreated group. After 4 days of anaerobic fermentation, the content of CH4 in the compound microorganism treated group was more than 50%, and fluctuated between 45% and 53% in the next 20 days. In the blank control group, the volume fraction of methane was stable at 36.7%. on the 6th day. The compound microbial strain HK-4 had a good hydrolysis effect on cellulose and hemicellulose in corn stalk and a higher straw degradation rate was achieved at lower temperature, which could improve the daily gas production and methane content. This economic and efficient pretreatment method provided new microbial resources for the utilization of straw resources in cold regions.