A supercritical CO2 reactor and a test system of creepage, diffusion and erosion of rock mass. The supercritical CO2 reactor includes a reactor body having a test chamber, a heating layer arranged in a side wall of the reactor body, a temperature sensor and a pressure sensor arranged in the test chamber, a sealing cover configured to seal an opening of the reactor body, a fixing component arranged on the sealing cover, a hydraulic loading component configured to apply an axial load on the specimen. The reactor body is provided with an air inlet/outlet pipe configured to communicate the test chamber with external environment. The air inlet/outlet pipe is provided with a air valve, and the fixing component includes vertical guide bars, an upper pad and a lower pad slideably arranged on the vertical guide bars. The hydraulic loading component includes a oil-loading tank and an axial loading rod.