## 2 Materials and Methods  
### Theoretical Analysis and Research Hypothesis  
The impact of environmental regulation on _GTFP_ is uncertain. Environmental regulation affects the development of _GTFP_ through the channels of the environmental cost, green technology innovation and so on. From the perspective of environmental cost brought by environmental regulation, with the intensifying of environmental regulation, the environmental cost faced by enterprises in the process of product production and processing will go up, and the profits of enterprises will decline gradually. It is difficult for enterprises to expand the production scale, which is not conducive to the expansion of reproduction, but also makes enterprises increase the amount of environmental pollution control [25]. From this point of view, environmental regulation will inhibit the improvement of _GTFP_. On the other hand, from the perspective of technological innovation, the strengthening of environmental regulation will promote enterprises to carry out green technological innovation [26], optimize and upgrade production processes to adapt to the high product quality standards [27], and reduce the waste of resources and environmental pollutants in the production process. Therefore, environmental regulation will promote the improvement of _GTFP_. As an important measure of environmental regulation, the environmental policy will also promote the development of _GTFP_. Specifically, it will promote the improvement of _GTFP_ through technological innovation, resource allocation and industrial structure. The APC Action Plan can enhance the upgrading of production technology, decrease pollution emissions, and significantly promote technological progress to drive _GTFP_. Local governments will strengthen the environmental supervision of enterprises according to the implementation of environmental policies, and enterprises need to adjust the industrial structure, product production, technological innovation to meet the requirements of the policy so as to improve the _GTFP_. Therefore, Hypothesis 1 is proposed as follows:  
**Hypothesis 1 (H1). **_The APC Action Plan will promote the improvement of regional_ GTFP. The intensity of environmental regulation is diverse in different regions. The regions with more pollutant emissions will be subject to greater environmental regulation intensity, thus enhancing more the local environmental level and improving the quality of people's life. For industries with varying degrees of pollution, environmental regulation will have different levels of constraints and penalties, so the impact on the TFP of the industry is heterogeneous [28]. The imbalance of economic development level, industrial spatial structure and greening protection level among different regions is also one of the significant reasons for the regional heterogeneity of the influence of environmental regulation on _GTFP_. Similarly, the environmental policy will also have a heterogeneous impact on TFP at different enterprises, industries and regional levels [6; 29]. According to the difference of pollutant distribution, the environmental policy will also set up pilot areas and non-pilot areas, and the policy effect of pilot areas will be better than that of non-pilot areas [11]. Therefore, Hypothesis 2 is proposed as follows:  
**Hypothesis 2 (H2). **_The impact of the APC Action Plan on_ GTFP _in different regions has regional differences._  
There is a complex relationship among environmental regulation, industrial structure and _GTFP_. On the one hand, environmental regulation can promote the rational adjustment of industrial structure, reduce the proportion of high energy consumption and high pollution industries at first. Besides that, it can speed up green technological innovation, improve air quality and reduce pollutant emissions. These measures have a significant impact on _GTFP_[21]. On the other hand, the adjustment of industrial structure may not play a role in protecting the environment.