Abstract: To solve the problem of fair benefit distribution among provinces in regional electricity market joint clearing, this paper proposes a regional electricity market gain allocation mechanism that incorporates energy-reserve joint clearing. First, a regional electricity market joint clearing model is constructed with the objective of minimizing the total operational cost of the entire network, which coordinates the optimization of energy production, reserve capacity, and inter-provincial transmission costs. Second, based on Shapley value theory, a gain allocation method is designed to quantify the marginal contribution of each province in joint operations, with further refinement to the levels of power generators and consumers to ensure fairness in benefit distribution. Finally, simulation verification is conducted on a three-region interconnected system. The results show that compared to traditional independent clearing models, the proposed joint clearing mechanism can reduce the total system cost by approximately 3% and decrease load shedding by about 80%. The research results provide theoretical support for the collaborative operation and benefit allocation of regional electricity markets.