Abstract: China's small reservoirs have a large quantity and a wide range. Due to historical reasons and the basin characteristics of the small reservoir, the problem of flood safety risk in the reservoir itself and downstream areas is prominent. The safety of small reservoirs is the key to the flood control of China's reservoirs during rainy seasons. Aiming at the needs of small reservoirs in terms of accuracy, timeliness and taking into account their own and downstream three aspects, this paper proposes an early warning method combining real-time rainfall, forecast rainfall, real-time water level and flow early warning, and constructs corresponding early-warning index system, which has been applied in the construction project of small reservoirs early-warning system in Anhui Province.