Green growth policy is the institutional guarantee and important support for China to change economic growth mode and implement the concept of green development. As the direct participants and practitioners of implementing multiple policy instruments, the subject of policy implementation has a profound impact on the achievement of policy objectives and policy effects. Therefore, it is significant to establish and improve the coordination network of China′s green growth policy executive subject, and to study the evolution process and the evolution law of the policy subjects′ coordination function, so as to improve the policy system of China′s green growth and improve the efficiency of policy implementation.
    Starting from the first law-Environmental Protection Law of the People′s Republic of China (Trial Implementation) in 1979, this paper carries out a full-text search in the Pkulaw Information Base. After eliminating duplicate, irrelevant and extremely ineffective policy texts, 354 policies are finally obtained.
    Based on the four important conferences on green growth in China, this paper divides China′s green growth policy into four stages: policy initiation stage (1979-1994), policy refinement stage (1995-2007), policy turning stage (2008-2015), and policy systematization stage (2016-).
    After summing up China′s green growth policy according to the above four stages, policy executive subjects are extracted, and the co-occurrence matrix of policy executive subjects is constructed. Based on the social network analysis method, the collaborative network of China′s green growth policy executive subjects is studied. On the basis of network map, this paper describes the evolution of collaborative network structure of green growth policy executive subjects in China from 1979 to now by measuring network structure indicators. Generally speaking, the network cohesion index and network density are rising overall, but the values of each stage are low. These indicate that the coordination effect among the China′s green growth policy executive subjects is weak as a whole, and the communication and coordination effect among the policy executive subjects need to be improved urgently. In these four stages, China′s green growth policy executive subjects show the network structure characteristics of "overall loose-centralized individual", "overall expansion-central equilibrium", "overall high-efficiency-multi-center compact", "overall stability-regional coordination".
     By establishing a two-dimensional "breadth-strength" matrix, the roles of policy executive subjects in the network can be divided into four types: high-breadth-high-strength (HH), high-breadth-low-strength (HL), low-breadth-high-strength (LH) and low-breadth-low-intensity (LL). In the policy initiation stage (1979-1994), the State Council, public institutions and local people′s governments have a high degree of breadth and intensity in the coordination network, which belongs to HH type. This indicates that the implementation of green growth policy mainly depends on government departments in the initial stage. In the policy refinement stage (1995-2007), the State Council is still in an absolute dominant position to coordinate multi-stakeholders. The Ministry of Environmental Protection has increased the scope and intensity of coordination, with more and more partners and more influential departments. The role of individuals, enterprises and the Ministry of Finance in green growth policies has also been strengthened. In the policy turning stage (2008-2015), the Ministry of Environmental Protection replaced the State Council, leading other policy executive subjects in the coordination of breadth and strength and becoming the most authoritative core subject. Individual behavior is more influenced by policy supervision and coordination with other subjects. The promotions of the Ministry of Finance, the Ministry of Land and Resources, the Ministry of Water Resources and the National Development and Reform Commission show that the government departments have clear powers and responsibilities during this period. Policy systematization stage (2016-): During this period, the Ministry of Environmental Protection is still at the absolute core of the network, and has absolute control and coordination power in the process of formulating and implementing green growth policy.
    Through the network evolution analysis of the policy subjects, it can be found that the core subjects influencing the coordination evolution network of China′s green growth policy in different periods are the State Council, the Ministry of Environmental Protection, the local people′s governments and individuals. This paper ranks the network subjects with the index of degree and degree centrality, and discusses the role and function evolution of subjects in the network by eliminating the change of the relevant network structure index. In the policy initiation stage (1979-1994), the importance of the four executing subjects in the network is the State Council, the local people′s government, the Ministry of Environmental Protection and individuals; in the policy refinement stage (1995-2007): the State Council, the Ministry of Environmental Protection, the local people′s government and individuals; in the policy turning stage (2008-2015): the Ministry of Environmental Protection, the State Council, the local people′s government and individuals; and in the policy systematization stage (2016-): the Ministry of Environmental Protection, the local people′s government, the State Council and individuals.
     The conclusions of this paper are as follows: (1) The number of China′s green growth policies is increasing, the number of policy executive subjects involved in is increasing significantly, the network connection frequency, network cohesion index and network density are generally rising, and the average distance of nodes is decreasing overall, indicating that in the process of growth policy implementation, the coordination between the subjects is more and more frequent, and the network stability and information transmission rate increase. In addition, the overall structure of China′s green growth policy implementation entity′s coordination network has changed from independent to centralized and stable, with a strong dependence on core entities and multi-agents. (2) The State Council, the Ministry of Environmental Protection, local people′s governments and individuals are the key core subjects in the coordination network. With the advancement of government system reform and the requirements of the era of green development, the Ministry of Environmental Protection has gradually replaced the State Council in playing a leading role in the network, and the State Council has gradually changed into a coordinated support position. The role of local people′s government in facilitating communication has been highlighted and individuals in the network mainly play the role of support and cooperation.
    Based on the above, this paper gives some suggestions in the following aspects: (1) Enhance the awareness of the rights and responsibilities of the policy executive subjects, deepen understanding of the green development strategy, and promote the development of the network to the multi-agent equilibrium coordination while ensuring the overall stability. (2) Continue to play the leading, organizing and connectivity functions of the core subjects in the network. In particular, it is necessary to strengthen the overall leading position of the Ministry of Ecology and Environment in the policy system. (3) Strengthen the network connectivity function of the coordination weak subjects and improve the coordination degree of the overall network.