The utility model provides an automatic device of purifing of super supercritical carbon dioxide system operation in -process, including the large capacity gas holder, the gas holder intake pipe, thegas holder outlet duct, the jar body and purification cavity valve, the purification cavity, purification cavity drain tap, miscellaneous gas discharges the export, gaseous percent concentration instrumentation, because among the super supercritical carbon dioxide circulation system, foreign gas is less than carbon dioxide in the same pressure temperature lower density, set up the purification cavity at the top of large capacity gas holder, under gaseous percent concentration measuring instrument and control system's automatic control, break -make through the cavity both sides valve of purifing, separate foreign gas from circulation system gradually, realize the promotion of working medium purity in the super supercritical carbon dioxide system, the number of times that adopts the carbon dioxide evacuation when at every turn starting can the lowering system be being built to the method, reduce the loss of carbon dioxide working medium, make the carbon dioxide purity in the super supercritical carbon dioxide system reach design service requirement.