Anaerobic digestion of chicken manure was carried out in this study basing on central composite design to identify the most optimal strategy for biochar supplementation. Model of cumulative methane production (CMP) was established by using response surface methodology. The optimal conditions predicted accordingly, including manure loading of 51.8 g VS/L, biochar dosage of 3.3% VSmanure, and cellulose loading of 98.0 g VS/L, were expected to maximize CMP, i.e., 294 mL/g VSmanure. The results also demonstrated that biochar dosage and its interaction with manure loading were key factors with significant impact on CMP. Biochar dosage higher than 3.5% VSmanure was observed to weaken the transformation of organic substances to methane. Higher dosage of biochar could considerably reduce concentration of organic acids, total ammonia nitrogen, as well as soluble salts. Verification experiment supported validity of the optimal strategy and provided data for cost assessment, which showed positive cost balances from biochar supplementation.