The most important feature of cascaded hydropower investment, intertemporal optimization, is neglected to some extent. This paper focuses on how to make an optimal decision on intertemporal investment based on the case of cascaded hydropower. I incorporated intertemporal investment and financing constraints in dynamic programming, and proposed a new objective function. As a result, an intertemporal optimal dynamic model is established. The model highlights the fundamental framework of dynamic programming on cascaded hydropower development. The framework is robustly suitable to improve investment efficiency with respect to intertemporal optimization.