The invention discloses an automatic power generation control method for cascade hydropower stations. The automatic power generation control method is characterized in that each cascade power station is controlled according to a given cascade output operating mode in dispatching and limiting cascade output. The automatic power generation control method includes steps of firstly, calculating the maximum output Nmaxk of an ith-stage power station, determining load distribution among the power stations, sequentially comparing a given dispatch output N with the maximum output of each of power stations at each stage from the upstream and the downstream and the value of Nmaxk, stopping judgment when the N is smaller than or equal to the Nmaxk, and determining load-distribution power stations as the power stations from the first to the kth stage; finally, calculating distribution output of the power stations according to the flow balance principle. Output requirements are met by operation of the least power stations, operating cost of the cascade power stations is reduced, and the upstream power stations are given preference to load distribution; load is distributed for the power stations at various stages in inverse proportion according to water consumption rate of the power stations, and after-distribution values are subjected to rationality verification; automation degree of high-cascade small serial hydropower stations can be improved, power generation benefits are increased, safety operation level of the power stations is improved, and labor intensity of operators is lowered.