Abstract: Cap-and-trade is one of the effective measures to control carbon emissions. China has launched a national carbon emission trading market in 2017. Carbon quota trading is divided into two ways:listed trading and agreement transfer. Therefore, under the two internal and external carbon quota trading paths, how to choose the carbon trading path and carbon emission reduction investment decision is an urgent problem to be solved for the member companies of the supply chain. A two-stage supply chain consisting of a single manufacturer and a single supplier is considered.Manufacturer can meet its carbon emission allowance requirements and have surpluses through carbon emission reduction investment, while the supplier's carbon emission allowance is insufficient.In the context of a perfect carbon quota trading market, supply chain member companies need to choose between the external carbon trading path and the coexistence path of internal and external carbon quota trading.Under different trading paths, corporate emission reduction decisions and internal and external carbon trading prices will have different effects on corporate profits. The trading conditions of internal and external carbon quotas, corporate emission reduction strategies, and profit influencing factors are analyzed by establishing a Stackelberg game model followed by manufacturers leading suppliers. An example analysis is carried out on the data of a manufacturing supply chain member company to verify the validity of the conclusion. The research results show that under the external carbon trading path, the emission reduction decisions of upstream and downstream enterprises in the supply chain affect each other, and when the unit carbon emission and the carbon emission reduction cost coefficient are equal, the carbon emission reduction rate of upstream companies is twice that of downstream companies; simultaneous internal and external carbon quota transactions can lower the wholesale price of intermediate products, increase the carbon emission reduction rate of member companies in the supply chain, and increase corporate profits.The calculation example finds that only when the enterprise carbon quota and the internal carbon transaction price are within a certain range can the internal carbon transaction be reached. At this time, the manufacturer will share the supplier's carbon emission reduction costs. Therefore, when the conditions for coexistence of internal and external carbon trading paths can be reached, the supply chain enterprises jointly formulate internal carbon trading prices can reduce the wholesale price of intermediate products, increase the order quantity of intermediate products and corporate profits; when formulating carbon quota policies, the government should appropriately relax restrictions on manufacturers' carbon quotas, encourage internal carbon trading, and promote carbon emission reductions in the supply chain. In this paper, the above points are taken into account, which can be used for reference in the same type of research.

Key words: supply chain management, carbon trading path, carbon quota trading price, carbon emission reduction