Achieving the goal of“carbon peak and neutrality”has led to a rapid increase in the penetration rate of clean energy in the smart grid, which also requires the public buildings in the smart grid to have the ability to respond to demand, and the load of heating, ventilation and air-conditioning（HVAC）systems cannot be underestimated in the total load of public buildings. For the sake of reducing the load of the public building and achieving the effect of “supply on demand”, first of all, for the public building, its energy systems, heat balance of the building and the HVAC system are modeled, and based on the model a two-stage scheduling scheme is proposed. The proposed scheduling scheme aims at minimizing the cost of building electricity consumption while maintaining indoor environmental comfort, and controls the HVAC system to get the best day-ahead scheduling plan. Then, in the real-time scheduling stage, the optimal scheduling scheme is completed with the goal of reducing the carbon emissions during the normal operation of the public building. The effectiveness and economy of the proposed new optimal scheduling scheme are verified by the simulation of an actual public building.