The cogeneration system of heat, power, and biogas (CHPB) driven by renewable energy provides an effective solution for carbon emission reduction in rural China. Starting from fully meeting the energy demand of 17 new rural residential households in Lanzhou, considering the annual dynamic local climate change, energy consumption characteristics, and environment parameters, a model of environmental benefit index for the CHPB system is constructed. The concept of emission factor is used to quantitatively analyze the environmental benefits of the system. The equivalent CO2 emission factor is defined to connect emissions with energy output, evaluating the environment-friendly potential of energy supply system. Compared with the conventional systems of independent power and thermal generation, the year-round characteristics of CO2 emission and emission structure chart of the proposed system are analyzed. The results show that the total CO2 emission and the average equivalent CO2 emission factors of the conventional and CHPB system are 85.45t, 1.53 kg/kWh, and 308.46t, 0.22 kg/kWh, respectively. The maximum CO2 emission reduction ratio of the CHPB system is 113.47%. Anaerobic digestion technology is employed to consume biomass feedstock, which reduced CH4 emission (equivalent to 86.36t of CO2 emission reduction). Five typical cities were selected to study the regional adaptability of the system and analyze environmental benefits. The results indicate that the CHPB system has the best environmental performance in Guangzhou, where the average CO2 emission reduction rate is 103.52%.