To extend the shelf life of button mushrooms, the optimal fumigation doses for hydrogen gas treatment were screened through sensory evaluation, combined with browning index and weight loss rate in this study. Then, using H₂ fumigation combined with polyethylene film packaging as a control, changes in the sensory quality, reactive oxygen species, browning-related enzyme activity and the nutritional quality of mushrooms treated by H₂ fumigation combined with nano-film packaging (H₂ + NA) during low-temperature storage were dynamically tracked. The preservation effect of H₂ + NA on mushrooms after harvest was investigated, and its mechanism was also analyzed. The storage validation test showed that the optimum H₂ fumigation time was 2 h, and the H₂ + NA-treated mushrooms had a fuller appearance, maintained whiteness well, showed a slow increase in reactive oxygen species, antioxidant enzyme activities remained at high levels, a high retention rate of protein content was observed, and there was a good antibacterial effect. This study indicates that H₂ fumigation combined with nano-film packaging can improve the storage quality of button mushrooms and may prolong low-temperature shelf life by 4–5 d compared to conventional commercial polyethylene film packaging.