Straw is one of the widely available renewable biomass resources. However, due to the difficult degradability of the lignin structure, wet anaerobic fermentation is generally not highly utilized for straw at present. In this study, Phanerochaete chrysosporium, a white-rot fungus, was co-cultivated with anaerobic sludge under microaerobic conditions to investigate its effect on methane production from straw in wet anaerobic fermentation. The results showed that the substrate methane yield (75.76 mL/ g VS) and TCOD removal in the co-culture group increased by 45% and 37%, respectively, compared to the non-co-culture group at 0.6 mg/ L dissolved oxygen. Electrochemical analysis revealed that co-culture effectively increased the sludge capacitance by 182.9%. The introduction of Phanerochaete chrysosporium made the straw easier to digest and produced electroactive substances, which intensified the humification process and extracellular electron transfer, and consequently increased methane production. Effective utilization of straw without pretreatment was achieved in this study, providing a reference for further straw resource recovery.