Abstract: This paper selects a large hydropower station in the upper Yangtze River as a case. Life cycle assessment was used to estimate its greenhouse gas (GHGs) emission according to the standardized processes (ISO14067) for carbon footprint quantization, focusing on the difference before and after the impoundment from three stages, i.e. construction, operation and decommission. Carbon emissions factors kW?hand energy payback ratio are selected as the indicators of cleanliness and quality. The results showed that: the carbon footprint of the hydropower station was 5417 million tons CO2eq, carbon emission kW?hfactor of the hydropower station was 70-131 g CO2eq/kW?h, and energy payback ratio was 2364. Compared with other kinds of power plants and other hydropower stations with reservoir, the carbon footprint is obviously lower and energy payback ratio is significantly higher. This implies the high quality and cleanliness of hydropower resource in the Southwest China. We came to a conclusion that hydropower development may promote the energysaving and emissionreduction; life cycle assessment (LCA) is applicable for analysis on carbon footprint of hydropower project. Key words：upper Yangtze River; hydropower; greenhouse gas; life cycle; uncertainty