The invention discloses a photovoltaic capacity configuration method suitable for a cascade water-light complementary energy power generation system. The photovoltaic capacity configuration method comprises the steps: a peak load curve and a base load curve of a typical load of the power generation system is generated; a photovoltaic power generation output probability model based on k-means is established; based on the peak load curve, the base load curve and the photovoltaic power generation output probability model and through establishing an operation simulation model of the cascade water-light complementary energy power generation system, the power generation income of the complementary energy power generation system can be calculated; based on the calculated power generation income and through establishing an investment cost income of the complementary energy power generation system, the photovoltaic installed capacity with the maximum net income is selected as the optimal configuration capacity of the power generation system. Thus, configuration of photovoltaic capacity of a cascade hydropower energy base can be achieved, resource waste caused by excessive photovoltaic investment is avoided, and meanwhile the investment income of a cascade water-light complementary energy power generation system is maximized.