This paper presents a Rolling Horizon Control (RHC) model to evaluate the Effective Forecast Horizon (EFH) of 10 days forecasting inflow derived from Quantitative Precipitation Forecasts (QPFs) and Effective Decision Horizon (EDH) for hydropower generation. This paper takes the Huanren hydropower reservoir located in the northeast of China as a case study. Firstly, the 10 days forecasting inflows are derived from the QPFs. Then the hydropower generation processes are simulated by the RHC model, and the performances of the hydropower generation with different EFHs and EDHs are evaluated, respectively. The results show that: (1) the RHC can adapt to varying conditions by re-optimizing the decisions during the EFH. (2) with the EFH increasing, the hydroelectric reliability increases and the efficiency decreases, while the efficiency and reliability are improved with shortened the EDH.