The invention relates to a method for preparing high-pressure gas-phase carbon dioxide through high-pressure powdered coal gasification. The method comprises the following steps: pre-cooling a raw material gas by using cold energy generated in a low-temperature methanol washing process, performing deep cooling separation so as to prepare a medium-pressure liquid CO2, pressurizing the medium-pressure liquid CO2 by using a low-temperature liquid pump, recycling the cold energy of the medium-pressure liquid CO2 by using the low-temperature methanol washing process, gasifying the medium-pressure liquid CO2 to generate high-pressure gas-phase CO2, and feeding to an upstream powdered coal gasification unit. Compared with the prior art, the method has the advantages that power consumption of gas-phase CO2 compression is greatly reduced, with the combination of the low-temperature methanol washing process, the cold energy of the liquid CO2 is recycled, the load of later low-temperature methanol washing decarburization and public project consumption are reduced, and the economical efficiency of a substitute natural gas technique is greatly improved.