In this paper, the simplified algorithms for quantitative calculation of drought resistance capacity are proposed under two kinds of commonly used data conditions: (1) available monthly runoff data and corresponding monthly or annual water supply-demand data, and (2) available monthly runoff data and water supply-demand data with different guarantee probabilities (50%, 75%, 90%, 95%, 97%, etc. ) for water resources planning. The drought resistance capacity is determined based on the relationship between the level index of drought resistance capacity and inflow frequency. A calculation example is given, which can provide references for further study and applications.