Abstract: Under the background of increasingly severe resource and environmental constraints, how to promote green development and promote the harmonious coexistence between man and nature has become a key issue on China’s development road. Through the measurement and differentiation research of China’s green development efficiency, the government can better grasp the current situation of China’s green development, and then the realization of sustainable economic development can be accelerated. Firstly, takes 30 provinces in China as the research object and introduces the by-production technology under the DEA framework to measure the green development efficiency in China. Then, uses Dagum Gini coefficient to further explore the spatial differences in China’s green development efficiency and their sources. The results show that during the sample period, China’s green development efficiency based on by-production technology is generally high, and the average value of green development efficiency is 0.84, but there is still room for improvement; the regional gap of green development efficiency is significant and on the rise. The inter-regional gap is the most primary source, with an average contribution rate of 44.12%. The regional difference in green development efficiency in the western region is the largest; the largest inter-regional differences are observed in the eastern and northeastern regions. Therefore, it is necessary to strengthen exchanges and cooperation on green development among regions to achieve regional green coordinated development. Finally, puts forward countermeasures and suggestions based on the conclusions obtained, providing decision-making reference for the comprehensive green transformation of economic and social development, and helping to promote the unification of economic benefits and environmental benefits.