China produces abundant corn stover annually, and direct incorporation into farmland offers a cost-effective route. However, this practice suffers from slow decomposition, poor seedling growth, high disease incidence, and limited carbon sequestration. In this study, we investigated the effects of graphene oxide (GO) on straw degradation by Trichoderma harzianum (BJ9) and the underlying mechanisms. Our results demonstrated that GO at concentrations of 5, 25, and 50 mg/L significantly promoted the mycelial growth of BJ9, with promotion rates of 32.04%, 40.74%, and 39.51%, respectively, whereas GO at 100 mg/L inhibited colony development. A litterbag assay showed that 25 mg/L GO significantly enhanced straw degradation, increasing mass loss after 60 days compared to BJ9 alone. Enzymatic assays revealed that GO elevated cellulase and lignin peroxidase activities of BJ9: at 5, 25, and 50 mg/L, cellulase increased by 20.71%, 59.02%, and 48.57%, and lignin peroxidase by 18.31%, 39.13%, and 31.6%, respectively. Soil analyses demonstrated that GO + BJ9 co-application raised soil organic matter, total nitrogen, ammonium nitrogen, available potassium, available phosphorus, and humic acid relative to BJ9 alone. RNA-seq further corroborated these results, showing upregulation of multiple glycoside hydrolase family genes, indicating that GO induces key lignocellulose degrading enzyme expression in BJ9. Consequently, GO-supplemented treatments improved corn stover degradation efficiency and shortened decomposition time compared with the strain control. Collectively, these findings highlight GO as a functional nanomaterial that enhances fungal lignocellulose degradation, providing a basis for developing nano-enabled inoculants to optimize straw incorporation and promote resource utilization.