Abstract: In optimal dispatch for cascade reservoirs, the progressive optimality algorithm (POA) suffers from premature convergence caused by poor initial solution . To solve the problem, this paper explores the key factors that influence the global convergence behavior of POA and presents a variable period progressive optimality algorithm (VPPOA). This new algorithm adopts a progressive differential strategy and a variable period strategy to replace respectively the approach used for solution of two-period optimal problems and the two-period optimal strategy in traditional POA, so that it can overcome the premature convergence problem caused by poor initial solution. Simulation results of optimal dispatch for the lower Jinsha River show that the gain in total electricity generation from VPPOA optimization is 0.15% more than that from POA and VPPOA-optimized solutions are nearly the same as those globally-optimized. Thus, this algorithm significantly reduces computational cost and improves the optimal dispatch of cascade reservoirs.