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This study evaluated the performance of limited calcium peroxide (CaO2) addition in maintaining the system stability of anaerobic digestion using lignocellulose biomass as a substrate at high organic load rates. Results showed that an overloaded digester, which had been on the verge of system collapse, regained its stability after 20 mg/L CaO2 was periodically added. Especially, limited CaO2 addition significantly reduced the volatile fatty acid (VFA) concentration and restored pH levels, thus enhancing methane production from 24.6 ± 0.4 to 80.9 ± 0.7 mL/g·VS. By combining the reactor performance, carbon mass balance, cell vitality of the microbial community, and metagenomic analyses, this study found that limited CaO2 addition stimulated the aerobic conversion of the VFA precursor to CO2 for VFA level control by facultative bacteria, which triggered their higher energy metabolism. Additionally, after limited CaO2 addition, acetotrophic and hydrogenotrophic methanogeneses were both promoted.