A transcritical carbon dioxide air conditioning system for an electric bus comprises a compressor, a three-way valve, an external heat exchanger, a first drying filter, a second drying filter, an internal heat exchanger, a gas-liquid separator and a heat regenerator, an outlet of the compressor is connected with a first connector of the three-way valve, and a second connector of the three-way valve is connected with an inlet of the external heat exchanger. A third connector of the three-way valve is connected with an inlet of the in-vehicle heat exchanger, one path of an outlet of the out-vehicle heat exchanger is sequentially connected with the first ball valve, the first drying filter, the in-vehicle heat exchanger, the gas-liquid separator, the heat regenerator and an air suction port of the compressor, and the other path of the outlet of the out-vehicle heat exchanger is connected with the gas-liquid separator. A pure natural environment-friendly CO2 refrigerant is adopted, the problem that a pure electric bus is low in heating efficiency in winter is solved, combined valves such as a pressure release valve and a ball valve are adopted, the situation that the system is blocked or abnormal high pressure of the system is caused under other abnormal conditions is prevented, and the heat regenerator in the system can effectively increase the suction superheat degree of the compressor and prevent liquid impact of the compressor.