On the basis of systematically sorting out ecosystem service functions and accounting methods of the gross ecosystem product, focusing on the water ecosystem, relevant literature from 2004 to 2021 were selected for statistical analysis. Through screening out 14 indicators of the gross water ecosystem product in three categories, a gross water ecosystem product accounting system was established, and accounting methods and calculation formulas of different indicators were provided. Taking Xiangjiaba Hydropower Station as an example, the impact of the construction of Xiangjiaba Hydropower Station on the gross water ecosystem product was evaluated using the gross water ecosystem product accounting system. The assessment results show that the change in the gross water ecosystem product from 2011 to 2015 was 26.11893 billion yuan, including the change in material good value of 11.14940 billion yuan, the change in regulation service value of 8.48151 billion yuan, and the change in cultural service value of 6.48802 billion yuan.