To investigate the impact of hydropower development on the gross river ecosystem product, an accounting index system of gross river ecosystem product under hydropower development was constructed. With the Lancang River and Nu River used as typical rivers with and without hydropower development, the gross river ecosystem products of the rivers in 2016 and 2021 were calculated, and a comparative analysis was performed. The results showed that, with the price of 2021 used as the constant price, the gross river ecosystem product of the Lancang River increased from 116.561 billion RMB to 126.422 billion RMB during 2016 to 2021, and that of the Nu River increased from 38.553 billion RMB to 39.424 billion RMB. The regulation service value always contributed the most to the gross river ecosystem product. Hydropower development increased the values of hydropower energy and flood regulation of rivers, but reduced the values of sediment transport, habitat diversity, and carbon sequestration. Hydropower development significantly increased the gross river ecosystem product at a rate of 87 million RMB per year on average, promoting the value realization of river ecosystem products and producing significant social and economic benefits.