The present invention provides a radiation apparatus with capability of preventing heat convection, which comprises a blackbody furnace having a cavity therein and an air pressure adjusting unit. The air pressure adjusting unit coupled to the blackbody furnace for adjusting the air pressure of the open end of the cavity according to the temperature difference between the cavity and the outside environment. By means of the design of the present invention, it is capable of preventing heat convection between the cavity and the outside environment by utilizing the air pressure adjusting unit for controlling the air pressure status around the open end of cavity such that the blackbody furnace is stable for services of calibrations and tests.