Abstract: Based on the water balance equation, and combined with the daily average inflow and outflow data, the reservoir water level-area-volume curve and the daily meteorological data of Guanting Reservoir station, the numerical model of the water flow change and balance under different controlled conditions was developed. The detailed verification results of the reservoir water level and leakage flow from dam site showed that the simulation data of water level fit well with the measured data. The model was applied to calculate the water level, water surface area and water volume changes of Guanting Reservoir during 2002-2016. The flow revenue and expenditure (including precipitation, evaporation and leakage) and their proportions were analyzed in details under the original reservoir operation scheme. Different scenarios were furtherly set according to Yellow River Diversion Project and the new operation conditions of Guanting Reservior minimum ecological flow control method in recent years. According to the calculation of hydrological series conditions from 2002 to 2014, the related results showed that if there was no outer-basin water transfer, the outflow process from Guanting Reservoir could not satisfy the requirement of the minimum ecological flow discharge, meanwhile, part of the downstream river would dry up. If with 1.0×10⁸ m³ additional input water from Wanjiazhai Reservoir in Yellow River from March to May every year and 5×10⁷ m³water into Guanting Reservoir, the outflow of Guanting Reservoir could basically satisfy the requirement of the minimum ecological flow.