## 4 Further Discussion
### Mechanism Analysis
#### 4.1.2 Moderating Effect of the Optimization of Industrial Structure  
This paper analyzes the coefficient estimation of the interaction terms TtO1 and TtO2 between industrial structure optimization and policy so as to analyze the moderating effect of industrial structure optimization from the aspects of \"quantity\" and \"quality\". The regression results of the moderating effects for the \"quantity\" OIS1 and the \"quality\" OIS2 of the industrial structure optimization between Table 8 Columns (3) and (4) and Columns (5) and (6). The coefficient estimates of two interaction items TtO1 and TtO2 in Table 8 are significantly negative in Columns (3) and (4) and Columns (5)and (6), indicating that the high degree of \"quantity\" and \"quality\" of industrial structure optimization will weaken the promotion effect of the APCP Action Plan policy on _GTFP_[41]. Moreover, the \"quantity\" of industrial structure optimization weakens the promotion effect of environmental policy on _GTFP_ more than the \"quality\". From the comparison of the three interaction coefficients in Table 8, it can be seen that the moderating effect of the \"quality\" of industrial structure optimization is larger than that of industrial structure rationalization and that of the \"quantity\" of industrial structure optimization. The different emphasis of industrial structure has a heterogeneous moderating effect on the promotion effect of the APCP Action Plan on _GTFP_. From the mechanism analysis, it can be seen that the moderating effect of the industrial structure has two sides. On the one hand, the rationalization of industrial structure can enhance the promotion of _GTFP_ by the environmental policy. On the other hand, the high degree of \"quantity\" and \"quality\" of industrial structure optimization will weaken the promoting effect. At present, China is also carrying out the transformation and optimization of the industrial structure [42], shifting the focus of development from the primary industry to the second and third industries because the economic development is still dominated by heavy industry with high output value and high pollution. At present, the \"quality\" of the industrial structure optimization in China reflects the transition from the primary industry to the secondary industry. It is no doubt that the economic development of various regions largely depends on industry. Although this type of industrial transformation is an essential \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **OLS (1)** & **FE (2)** & **OLS (3)** & **FE (4)** & **OLS (5)** & **FE (6)** \\ \hline  & _InGTFP_ & _InGTFP_ & _InGTFP_ & _InGTFP_ & _InGTFP_ & _InGTFP_ \\ \hline TtR & \(0.161\)** & \(0.178\)** & & & & & \\  & (2.12) & (4.13) & & & & & \\ TtO1 & & & \(-0.256\)** & \(-0.266\)** & & & \\  & & & (\(-4.30\)) & (\(-3.62\)) & & & \\ TtO2 & & & & & \(-0.0791\)** & \(-0.0803\)** \\  & & & & & \((-3.96\)) & (\(-7.73\)) \\ Policy & \(-0.0168\) & \(-0.0104\) & \(0.627\)** & \(0.651\)** & \(0.0572\)** & \(0.0639\)** \\  & (\(-1.23\)) & (\(-1.06\)) & (4.40) & (3.68) & (5.26) & (6.61) \\ RIS & \(0.0133\) & \(0.0108\) & & & & \\  & (0.65) & (0.44) & & & & \\ OIS1 & & & \(-0.0761\)** & \(-0.0785\)* & & & \\  & & & (\(-1.99\)) & (\(-1.82\)) & & & \\ OIS2 & & & & & & \(0.0057\) & \(0.0075\) \\  & & & & & (0.68) & (0.78) \\ ytreat & & \(-0.0018\)* & & \(-0.00000141\) & & \(-0.0012\) \\  & & (\(-1.78\)) & & (\(-0.34\)) & & (\(-1.24\)) \\ Control variable & YES & YES & YES & YES & YES & YES \\ Individual effect & YES & YES & YES & YES & YES & YES \\ Time effect & YES & YES & YES & YES & YES & YES \\ \_cons & \(-0.0192\) & \(1.351\)* & \(0.184\)* & \(0.216\)** & \(-0.0223\) & \(0.907\) \\  & (\(-0.61\)) & (1.85) & (1.83) & (2.21) & (\(-0.80\)) & (1.34) \\ \hline N & 420 & 420 & 420 & 420 & 420 & 420 \\ \hline \hline \end{tabular} Note. *, ** and *** represent passing the significance test of 10%,5% and 1%, respectively, the same below.  
\end{table} 
Table 8: Test of the moderating effect of industrial structure on policy.