## 1 Introduction
The study by [19] implemented the incentive policy of time-of-use electricity price and carbon quota based on netload power and the results showed that this mechanism increased the effort of absorbing new energy, reduced the phenomenon of abandoning wind and solar power, and improved the on-site absorption capacity and the interests of both grid and load. Based on the theory of carbon emission flow, the above literature combined carbon trading and source-load coordination which is of great significance to the study of low-carbon scheduling of power systems. However, the carbon responsibility allocation based on the carbon emission flow theory is irrational due to the topology of the power grid and the heterogeneity of carbon emissions from power sources. This is because the matrix of the power injected into nodes and the carbon intensity matrix of each generator are involved in the process of solving the carbon intensity matrix of the user node using the carbon emission flow theory [20; 21]. For this reason, the user's carbon responsibility is not only related to electricity consumption. In the pool market environment, the carbon responsibility allocation based on the carbon emission flow theory is unfair to users with a higher carbon intensity of nodes. In order to reduce carbon responsibility, users respond to emission reduction by reducing or transferring load which will lead to a decrease in user satisfaction with electricity consumption [22; 23]. With the gradual opening of the electricity sales side market [24; 25; 26], the bilateral transaction mode emerges, providing a new way for demand side resources to participate in the power market. From the perspective of game theory, the literature [27; 28] pertaining to studies on the bilateral transaction modes between multiple power generators and large users provides references for the formulation of bilateral transaction mechanisms. The studies in [29; 30] analyzed the energy-saving and emission reduction benefits of four bilateral trading modes, including power generation rights trading, trans-regional and trans-provincial power trading, and direct power purchasing trading for large users,providing a theoretical basis for the bilateral market to help the low-carbon construction of the market. In [31], the impact of pricing strategies of generators participating in spot and bilateral markets on other market participants was discussed, maximizing the benefits of each power generator participating in the market under the game environment and achieving the economic objectives of the market. To sum up, bilateral transactions promote new energy consumption and carbon emission reduction by introducing competitive power sellers and gradually opening up the user's right to choose [32; 33]. Therefore, bilateral trading realizes the direct interaction between the two sides of the source and load, creates a place of free trade for users and power generators, and provides a new way for users to reduce their own carbon responsibility through market means. In summary, from the perspective of emission reduction, this paper introduces the bilateral trading mode between generators and users and proposes a bi-level emission reduction model of the hybrid electricity market incorporating source-load coordination and carbon emission flow. Finally, the multi-case comparison verifies that the user response mechanism under the hybrid electricity market has the benefit of emission reduction. The main contributions of this paper are as follows:  
1. Based on the source-load coordination and the carbon emission flow theory, this paper proposes a bi-level emission reduction model of the hybrid electricity market;
2. Introducing the bilateral trading mode, the trading mechanism of the hybrid electricity market is constructed, and thus, a new way for users to respond to emission reduction is provided;
3. Based on the IEEE9-node system, the effectiveness of the emission reduction model in the hybrid electricity market is verified.