Abstract: Sewage sludge and food waste have been generated to seriously threaten sustainable source management, particularly with the rapid urbanization. Heavy metals can persist in the environment and then bioaccumulate in soil and biota in the municipal sewage sludge. The safe use of sewage sludge products can also be restricted due to the long-term ecological and health risks. In this study, the bio-conversion technology of the black soldier fly (Hermetia illucens) larvae (BSFL) was applied to enhance the efficiency of the sewage sludge treatment, and then reduce the environmental risks. Four types of organic wastes—kitchen waste, fruit and vegetable residues, soybean pulp, and wheat bran—were mixed with the sewage sludge at a 1:1 ratio. The nutrient-deficient substrates was improved enhancing the growth and bioconversion performance of BSFL. Furthermore, the BSFL growth and bioconversion were assessed via the waste reduction rate, biological conversion rate, and feed conversion rate. Heavy metal and soil nutrient elements were quantified to evaluate the compost safety in BSFL and frass, according to the residual heavy metal levels. The reduction rates of the wastes ranged from 42.44% to 74.48% in the four treatment groups, indicating the substantial substrate degradation during BSFL bioconversion. Compared with all the initial mixed substrates, the BSFL frass exhibited notable decreases in the organic matter content and carbon-to-nitrogen ratio. The total nutrient content increased to 5.35%~6.31 %, thus represented by the sum of total nitrogen, total phosphorus, and total potassium. Its potential was enhanced as an agricultural amendment. Different substrate composition was significantly dominated by the BSFL growth performance, biomass yield, and conversion efficiency, which in turn influenced the BSFL frass' physical and chemical properties, as well as the nutrient content. Among the tested combinations, the wheat bran-sewage sludge mixture was achieved in the most favorable conditions for the BSFL development. Specifically, there was the superior performance of the larvae biomass accumulation and waste reduction rate. Heavy metals migration analysis revealed that the BSFL was used to modulate the metals' behavior in the substrate using various reactions, such as active absorption, selective retention, physiological regulation, and excretion. The bioaccumulation coefficients of the heavy metals were ranked in descending order of Cd > Cr > Pb > As. Among them, the cadmium (Cd) was the highest enrichment, followed by Chromium (Cr), lead (Pb), and arsenic (As). The concentrations of Cr, Cd, Pb, As, zinc (Zn), and copper (Cu) were significantly lower in the final BSFL frass than those in the initial substrates. The effective removal of the heavy metals was realized under different uptakes during bioconversion. However, the BSFL frass remained rich in the essential soil nutrient elements, such as calcium (Ca), magnesium (Mg), manganese (Mn), and sodium (Na), indicating its promising potential for agricultural applications. Meanwhile, the BSFL shared the promising potential for resource utilization in the animal feed and the frass. The systematic assessment was also safely applied to the agricultural land, such as the cultivated land, garden plots, and grassland. The BSFL bio-conversion greatly contributed to the treatment efficiency of the municipal sewage sludge and kitchen waste, fruit and vegetable residues, soybean pulp, and wheat bran. The findings can offer valuable theoretical and practical insights for the resource recovery and sustainable utilization of the food waste-sewage sludge mixed substrates. Furthermore, the compost products can be safely applied to mitigate the environmental risks, thereby promoting the eco-friendly disposal of the organic wastes.