Abstract: In the optimal operation of hydropower stations, an optimal decision obtained by deterministic optimization for a certain period is influenced by the inflow in the adjacent periods. Due to the instability of inflow, the operation rules for some periods often become extremely complicated, resulting in a difficulty in rule derivation. To solve this problem, this paper presents a new idea of extracting staged operation rules using explicit mechanism and a practical method that divides the scheduling period into two parts, a stable period and a transition period, according to the rule patterns throughout the scheduling period, and then adopts different method of rule derivation for each period. For the transition period, we introduced a strategy of period-by-period inflow classification for an effective division of the upper and lower scheduling lines obtained by optimal decision, based on the inflow characteristics. To verify the robustness of this method, a case study was made for the Tianshengqiao-I hydropower station, and results show that the method is effective and advantageous in derivation of operation rules.