Based on the normal operation charts of cascade reservoirs, we proposed a mathematical model of optimal operation chart aiming to reach at the maximum value of annual average electricity generation. In this regard, we suggested a solving algorithm to reduce dimensionalities based on multiple iterations as follow: reduce spatial multi-reservoir dimensionality by iteration in reservoir turns; reduce multi-curve dimensionality by iteration in rule curve turns; and reduce multi-state dimensionality of rule curve with progressive optimality algorithm. Overall, results based on experiments considering Wananxi-Baisha cascade reservoirs as a case studies show that this optimum method provides optimal operation charts of cascade reservoirs in rational form as well as significant increases in electricity generation of the reservoir group while compared with traditional method.