Abstract: Drought-limited water level (DLWL) is an important indicator for early warning against droughts and can be used to guide the drought-relief operation at reservoirs. This study aims to build a determination algorithm to specify the DLWL for different types of reservoirs. We define the DLWL of a reservoir as the water level at which the water supply system reaches the critical point of drought and water shortage. By introducing the double layer of operation and guarantee periods as control parameters, a general algorithm for DLWL suitable for multi-year, annual, and seasonal regulation of reservoirs is proposed, which is used to form a reservoir drought-resistant operation strategy. The Zhangfeng Reservoir and Hechuan Reservoir were used to verify the feasibility and rationality of the double-layer sliding algorithm for the multi-year and seasonal regulation of reservoirs, respectively. The results show that by setting the DLWL, the serious water shortage in drought years can be effectively alleviated; the water shortage rate and period in each industrial sector can be significantly reduced. This study provides a general algorithm to the flood and drought disaster prevention department to set a DLWL and guide the drought-relief operation of the reservoir, which can provide the scientific basis and technical support required for drought prevention.