Abstract:    Since the reform and opening up, China′s industrial development model is characterized by high investment, high energy consumption and high emission. Although this development model has played a major role in economic growth, it has also brought serious environmental pollution problems. Therefore, promoting industrial green transformation has become the primary problem that the governments have to face to realize the China′s economy high-quality growth. The 13th Five-Year Plan points out continuing to strengthen the integrated ecological management process. In the meanwhile, the 19th National Congress of Communist Party of China also emphasizes building a market-oriented green technology innovation system. These all indicate the way for the future development of the industry. Accordingly, this paper focuses on the relationship among environmental regulation, clean-technology innovation and industrial green transformation. The conclusions have important theoretical and practical guiding significance for formulating reasonable environmental supervision policies and clean-technology innovation incentive policies to promote industrial green transformation.
    The existing research draws relatively more attentions on the relationship between environmental regulation and technology innovation and the discussion of combining the environmental regulation and clean-technology innovation is less during the process of analyzing the core driving elements of industrial green transformation. Furthermore, there are big differences in the research conclusions. Some scholars believe that environmental regulation is the main strength driving China′s industrial green transformation，and some other scholars do not agree with this view. The possible reason why the research conclusions are different lies in the nonlinear effects of environmental regulation on the industrial green transformation．
   In the content of research, the main work and contributions of this paper mainly focus on the following two aspects: Firstly, this paper argues the complex non-linear relationship between environmental regulation and industrial green transformation, and constructs panel threshold model to validate the conclusion. Secondly, environmental regulation, clean-technology innovation and industrial green transformation are integrated into the uniform framework, and then this paper deeply analyzes the interactive effect of environmental regulation and clean-technology innovation on the industrial green transformation. Meanwhile, this paper also tests the different interactive effect of environmental regulation and clean-technology innovation on industrial green transformation between clean industry and pollution industry.
   According to the above analysis, this paper tests the impact mechanism of environmental regulation and clean-technology innovation on industrial green transformation based on panel data of 26 industrial sectors in China from 2005 to 2013. By constructing the panel threshold regression model, this paper tests whether the relationship between environmental regulation and industrial green transformation is nonlinear. This model not only determines the number of threshold values automatically, but also determines the specific threshold value. This paper also examines the interactive effect of environmental regulation and clean-technology innovation on industrial green transformation by introducing interactive term between environmental regulation and clean-technology innovation into the panel data econometric model. 
  The main research conclusions of the paper are as follows:
  Firstly, there is a triple threshold effect between environmental regulation and industrial green transformation. As a result of threshold effect, lower environmental regulation has a significant positive effect on industrial green transformation, and higher environmental regulation has a negative effect on industrial green transformation. The relationship between environmental regulation and industrial green transformation is inverted U-shape through innovation compensation effect and following cost effect. On one side, environmental regulation improves the industrial enterprises green productivity growth level, and presents the innovation compensation effect. On the other side, when environmental regulation is very high, environmental regulation also reduces the industrial enterprises investment in R&D, and presents the following cost effect. 
   Secondly, environmental regulation can positively influence the effects of clean-technology innovation on industrial green transformation. Under the pressure of government environmental regulation, enterprises will shorten the time for equipment renovation. Then, clean-technology innovation plays the role of energy-saving and emission reduction. In addition, environmental regulation can change consumer choices. Affected by environmental regulations, consumers′ awareness of environmental protection has increased, and they have gradually accepted green products and their demand has continued to expand. Driven by market demand, enterprises are willing to produce green products. Once some enterprises benefit from the green products, and the positive feedback loop kicked in. This will attract more enterprises to use clean-technology to produce more green products, and accelerate the whole industry toward green development ultimately. 
   Thirdly, the interactive effect of environmental regulation and clean-technology innovation on industrial green transformation has an industrial heterogeneity. Compared with polluting industry, the interactive effect is more obvious in the clean industry. There are two reasons to explain this result. The environmental regulation squeezes fewer resources for clean industry. Therefore, the clean- technology innovation will better promote industrial green transformation with more financial support. Besides, the government′s environmental supervision can enhance consumers′ preference for green products. The clean industry has the advantage of clean-technology to accelerate the production of green products, which is conducive to improving the competitiveness. By forming a virtuous circle of "clean production technology, green products, market competitiveness", the interactive effect of environmental regulation and clean-technology innovation on industrial green transformation is more obvious in clean industry. 

Key words: environmental regulation, clean-technology innovation, industrial green transformation, threshold effect, interactive effect