Abstract: The bed breeding of ducks has been widely used, but long-term breeding bedding would result in the accumulation of heavy metals and salts. Meanwhile, the bedding waste is not always completely mature, which would bring security risks to the reutilization of these bedding wastes. In this study, thermophilic microorganisms were inoculated during aerobic composting of bedding wastes, and the safe amount of composted bedding returned to the field was evaluated through a field experiment. The results show that the bedding wastes can be fully decomposed within 50 days of simple stacking with regular turning. Compared with the non-inoculation control, inoculation of 0.5% thermophilic microbial agent could significantly improve the degradation rate of organic matter, and the seed germination index was increased by 23.8%. The yield of muskmelon treated with 25% compound fertilizer N+75% composted bedding N was the highest, which was 8.17% higher than that of 100% compound fertilizer N treatment. The contents of vitamin C and soluble sugar in muskmelon fruit treated with 25% compound fertilizer N+75% composted bedding N were also the highest. Compared with 100% compound fertilizer N treatment, the composted bedding returning treatments increased the contents of soil organic matter, total nitrogen, ammonia nitrogen, available phosphorus and available potassium. However, the contents of Cr, Cu and Zn in the composted bedding returning treatments were increased by 3.15%, 11.65% and 10.17%, respectively. The soil electric conductivity was 40.19% higher than that of the 100% compound fertilizer N treatment. The contents of heavy metals in melon fruit and soil increased with the increasing proportion of bedding materials. This study provides an important basis for the efficient treatment and safe utilization of the bedding materials for meat duck breeding.