Abstract: Under the guidance of "carbon peaking and carbon neutrality", the low-carbon transformation of power system is imperative. Low-carbon demand response combined with time-varying price signal can guide users to adjust electricity consumption behavior to reduce carbon emission. However, the flexibility of different users varies greatly. It is difficult to guide low flexibility users to achieve carbon emission reduction only through the change of price signal, and the regulatory potential of highly flexible users is not fully released. To further release the carbon emission reduction potential on demand side through flexible transactions between users, this article proposes a demand side electricity-carbon coupling trading mechanism, aiming to further release the carbon reduction potential of highly flexible users through the redistribution of carbon emission responsibilities. However, according to the proportional sharing theorem, carbon emission responsibility is in a fixed proportion to electricity consumption, which limits its flexible transfer between users. This article proposes "virtual carbon storage" to make the carbon emission intensity of electricity in energy storage a controllable variable, achieving the free transfer of carbon emission responsibility among users. This article also takes the regional power system as the research scenario, comprehensively considering the cost of electricity bills, carbon emission, and load regulation costs, and introducing a proximal policy optimization algorithm to solve the optimal electricity consumption strategy for users. The simulation results show that compared to users only participating in the traditional electricity market, participating in the electricity-carbon coupling market and considering "virtual carbon storage" reduces carbon emissions by 31.9%, as well as significantly reduces users' electricity costs.