Currently, China's renewable energy power generation industry is facing problems such as mismatch between output and input, and regional imbalance in power generation efficiency. Measuring power generation efficiency and identifying the key constraints to improving it is an important way of exploring measures to improve power generation efficiency from a management perspective. This paper constructs a system of input-output assessment indicators for the efficiency of renewable energy generation in China, and evaluates and analyses the efficiency of hydro, wind and solar power generation in each province of China for the period 2016–2020 using the DEA game cross-efficiency model. The results show widespread inefficiencies and uneven regional development in the three renewable energy generation industries. The hydropower generation efficiency changed little, the wind power generation efficiency decreased slightly, and the solar power generation efficiency gradually increased. On this basis, the key factors affecting the efficiency of hydro, wind and solar power generation in China were analyzed separately through the Tobit model. The results show that natural resources, grid conditions, and inter-provincial power transmission are important factors in improving the efficiency of renewable energy generation. This paper also makes recommendations for improving the efficiency of renewable energy generation in China in terms of policy formulation, technology promotion and grid construction.