The invention relates to a method for obtaining high-temperature and high-pressure gas, belonging to the field of heat exchange. A high-pressure gas source section, a high-temperature and high-pressure combustion chamber and a Laval nozzle are provided. The method comprises the following steps: performing combustion reaction on high-pressure gas provided by the high-pressure gas source section in the high-temperature and high-pressure combustion chamber to generate high temperature; and through a pressurizing effect of the Laval nozzle, forming high pressure in the high-temperature and high-pressure combustion chamber, wherein by controlling the combustion reaction in the high-temperature and high-pressure combustion chamber and an outlet Mach number of the Laval nozzle, the temperature, the pressure and the components of gas in the high-temperature and high-pressure combustion chamber are adjustable. The invention can provide a novel method for obtaining the high-temperature and high-pressure gas; and by the method, the high-temperature and high-pressure gases can be generated through combination of different temperatures, pressures and components within the temperature range of 1800-3000K, the pressure range of 1-3MPa and the gas concentration range of O2: 1-10%, N2: 70-80%, CO2: 5-15% and H2O: 5-15%.