Abstract: There are the large number of small reservoirs in China, which have major risk of operation with high illconditioned and/or dangerous risk rate. The problem of flood security of small- scale reservoirs is still very prominent. A considerable number of small-scale reservoirs are in danger or collapse every year. In consideration of the characteristics of short forecast period and difficult early warning for small-scale reservoirs, based on the monitoring data of small reservoirs, real-time rainfall and meteorological forecast rainfall, the early-warning technology called“four-axis and three-phase”which can form a relationship between water level, storage capacity, rainfall receiving capacity and forecasted rainfall is adopted to improve the early warning ability of small-scale reservoirs. Practice has proved that: the rainfall information service and early warning system of small reservoirs based on meteorological and hydrological fusion technology can improve the information management efficiency of small reservoirs, strengthen the information security management of small reservoirs, effectively prolong the early warning and forecast period and improve the forecast and early warning ability, which is of great application value for the flood management of small-scale reservoirs.