Much attention has been paid to the environmental problem caused by poor efficiency of energy use. Most of all,we should realize the problem such as global warming and the frequent appearance of the " haze" weather. For sustainable development in all regions,it is necessary to take measure to solve the problem above,and undoubtedly,efficiency improvement is the route one must take to alleviate the contradiction between energy supply and demand and to alleviate the pressure of environmental protection. In recent years,it has been a matter of great concern on the ways of energy - saving and emission - reduction supported by financial system. How to relieve the financing constraints of enterprise technological innovation,and to improve the optimal allocation of regional resources,as well as the transmission path to push forward progress in energy - saving and emission - reduction, is question which is still worth discussing. Perfect financial system can provide strong support through scale expansion, structure adjustment and efficiency promotion for resources rational allocation and utilization. It is of guiding significance to grasp the current situation of energy efficiency in China and formulate effective financial policies to explore the impact mechanism and transmission path of financial development on energy efficiency. Chinas low regional energy efficiency is reflected in two aspects: usage and allocation. On the one hand,low technology level and extensive energy use have seriously affected the improvement of energy efficiency,high cost of equipment retrofits and technological innovations and the trade - offs of consistently low energy price make the company less efficient in internal energy efficiency development,Combining with a longer return on investment which causes serious external financing constraints. On the other hand,the substitution of elements that deviate from the optimal combination of factors makes the energy allocation efficiency decline,factor market imperfection,and the government's price control on primary energy causes the energy price to be seriously underestimated. The relative price distortion of capital,labor and energy makes the micro - enterprises usually lack of motivation for technological innovation or improvement under the trade -off of cost and revenue,continuing using low - cost energy for factor replacement to maintain production. Some progress has been made in theoretical research on the impact of financial development on energy efficiency both here and abroad,but there are still some limitations. Firstly,in terms of the selection of financial development indicators,the existing literature pays less attention to the systemic integrity of financial development,depicts financial development only from the perspective of scale,ignores the impact of changes in financial structure and improvement of financial efficiency on energy efficiency. Therefore,it makes the conclusion biased because it can not cover all the essentials of financial development. Secondly,there are abundant models to test the relationship between financial development and energy efficiency,but most of these models are linear ones. This paper argues the complex non - linear relationship between financial development and energy efficiency,which is resulted in the differences of regional resource endowment,economic level and industrialization degree. This non - linear relationship is also the main reason for the inconsistency of the existing literature on the direction and extent of the impact of financial development on energy efficiency.