Abstract  [Aim]  Feeding fermented mushroom bran to Allomyrina dichotoma larvae not only enables harmless treatment and efficient utilization of mushroom bran waste, it also effectively reduces insect rearing costs. This study aimed to determine how fermentation duration and population rearing density affect the conversion of mushroom bran by A. dichotoma larvae, providing theoretical support for biological control and utilization of mushroom bran by the beetle larvae. [Methods]  3rd instar larvae were raised at 29 ℃ for 40 days. The amount of mushroom bran consumed, feces excreted, and larval weight, were measured under different fermentation durations (10, 20, 30 and 40 d, respectively) and different rearing densities (20, 30, 40, 50, 60 larvae/case, respectively). [Results]  There was a significant increase in the ability of larvae to transform mushroom bran with increasing fermentation time. Food intake, the amount of feces excreted, and larval weight was (42.11±0.14), (30.12±0.40) and (8.21±0.26) g, respectively, in A. dichotoma fed mushroom bran fermented for 40 days. This result was significantly higher compared to the other treatment groups but not the control (P<0.05). There was no significant difference in the survival rate of the larva with increasing rearing density (P>0.05), but average weight gain, food intake, and feces excretion showed a significant downward trend. At a density of 30 larvae/case, average larval weight gain, food intake, and feces excretion was (5.20±0.06), (56.32±1.14) and (35.74±0.47) g, respectively. This result was not significantly different from the minimum density of 20 larvae/case, but it was significantly higher than the other density treatments (P<0.05). [Conclusion]  Based on our findings, the optimal fermentation time for the effective conversion of mushroom bran by A. dichotoma, is 40 days. To conserve resources, the population density of A. dichotoma should not exceed 30 larvae/case.