The invention discloses a flexibility evaluation method, device and apparatus of a power system and a storage medium. The method comprises the steps of calculating to obtain intraday net load output data according to historical load output of the power system and output of renewable energy sources; decomposing the intra-day net load output data into a plurality of fluctuation components accordingto a preset multi-scale decomposition algorithm of a WMMF filter; according to the fluctuation component, calculating to obtain the insufficient flexibility probability and the average flexibility cost of the power system; and evaluating the power system according to the insufficient flexibility probability and the average flexibility cost, and adjusting the power of the power system. By adoptingmultiple embodiments, the problems that the proportion of renewable energy sources cannot be evaluated and the influence of the flexibility cost on the flexibility adjustment of the power system cannot be evaluated in the prior art are solved.