Mandatory and voluntary emissions trading systems are effective market mechanism to curb climate change. China's mandatory emissions trading mechanism has incorporated some industries to promote enterprises to reduce carbon emissions consciously, the enterprises'compliance rate remains high,and overal carbon emissions and intensity of carbon emissions show a double downward trend within the scope of the pilot,while there are still a great number of enterprises outside the mandatory emissions trading mechanism,encouraging these enterprises to participate in the voluntary emissions trading mechanism to reduce carbon emissions actively is conducive to realize national carbon emission reduction targets smoothly and to promote green development of economy and construction of ecological civilization. Against the background,taking the enterprises outside the mandatory emissions trading mechanism as the research object,this paper employs the parameters of government compulsory emissions reduction probability and financial subsidy,constructs the dynamic game theory model,and analyzes the behavior choice of enterprises and governments. According to the market power of different enterprise,this paper explores the possible strategies to promote the participation of enterprises in voluntary emissions trading mechanism. It is proved that: ① Voluntary emissions trading mechanism is cost - effective for both government and enterprises,and it can promote enterprises to reduce carbon dioxide emissions. However,efficiency of implementing voluntary mechanism may be affected by the enterprises'market power. ② Government should have an important role in voluntary emissions trading mechanism and help enterprises to improve effects of voluntary reduction. ③ Given the social welfare loss is small,subsidy policy could fulfill supporting feature,enhance enthusiasm and reduction level of enterprises in voluntary emissions trading mechanism. Therefore,to enhance enthusiasm of participating in voluntary emission reduction and raise the level of voluntary emission reduction for enterprises outside the mandatory emissions trading mechanism,government should formulate precise and detailed voluntary emission reduction policies according to the types and characteristics of enterprises,and maintain a certain potential regulatory pressure to coordinate and guide,and if necessary,financial subsidies could be used to improve the level of voluntary emission reduction.