The regional discrepancies among various power systems are the preconditions for the integrated power system benefit. The national power grid has been formed initially. It provides the physical foundation for the benefit of integrated power system. Based on the analysis of resource distribution features of China and the generation structure features, the paper has reviewed the power grid development history and foreseen the development trends of the interconnected power system in China. The following integrated power system benefit has been analyzed: peak load regulation; hydro power and thermal power integration; cross-river basin adjustment; and scale merit, etc.