This thesis constructs an energy efficiency measurement system including economic benefit and environmental impact, and measures the energy efficiency level of each province in the Yangtze River Economic Belt under environmental constraints from 2001 to 2016. Through the horizontal and vertical analysis of panel data, it is found that the energy efficiency level of the cities in the lower reaches is higher than that of the cities in the middle reaches, and the cities in the middle reaches are higher than that of the cities in the upper reaches, which is suitable for the development of the Yangtze River Economic Belt. Longitudinally, energy efficiency shows a U-shaped trajectory over time. From 2001 to 2016, the energy efficiency level of Shanghai has been at the highest point on the right side of the U-shape, with Zhejiang, Jiangsu and Hunan provinces showing a complete U-shape change, Anhui, Jiangxi and Hubei provinces at the right side of the U-shape rising stage, and Chongqing, Sichuan, Guizhou and Yunnan provinces at the left side of the U-shape falling stage. By using the fixed effect regression model, this thesis makes an empirical analysis on the influencing factors of energy efficiency in the Yangtze River Economic Belt, and the results show that the industrial structure, the degree of opening up and the influence of the government have a positive effect on the improvement of energy efficiency, the energy consumption structure has a negative effect on the energy efficiency, and the technological progress has no significant effect on the energy efficiency.