Abstract: To improve the accuracy of clearing price estimation in electricity markets with multiple power sources under source-load uncertainty, this paper proposes a day-ahead market clearing price interval prediction model. The model considers the uncertainty of generation-side output characterized by multidimensional stochastic distributions and the impact of load-side demand response. Based on the physical clearing mechanism of electricity markets and the IEEE 30-bus power system, the model aims to minimize the total generation cost with the participation of hydropower, thermal, wind, and solar power. By solving the proposed model, the interval results of LMP and generation commitments can be obtained, taking into account source-load uncertainty. Case studies show that the proposed method improves bidding efficiency and generation revenue. Compared with traditional point forecasting methods, it achieves a 4.09% increase in overall economic efficiency and a 0.47% improvement in expected revenue. The results verify the feasibility and effectiveness of the model, providing reliable decision-making support for generators in formulating stepwise bidding and output strategies in the day-ahead market.