The invention discloses a black body cavity radiation source which comprises a liquid thermostat, a black body cavity, a temperature controller, a pump and a standard thermometer. The black body cavity and the temperature controller are installed in the liquid thermostat, the black body cavity comprises a cavity inner shell and a cavity outer shell, and the inner wall of the cavity inner shell and the inner wall of the cavity outer shell are coated with black diffuse reflection coatings. The cavity inner shell with the front end being a conical cavity and the rear end being a columniform cavity is coaxially installed in the liquid thermostat, and the cavity outer shell with the same shape as that of the cavity inner shell is installed outside the cavity inner shell to form an equally spaced hollow interlayer. The end surface of the cavity inner shell is connected with the outer wall of the liquid thermostat, a conical cavity opening of the cavity outer shell is communicated with a pump shell, the pump shell is communicated with the liquid thermostat through the opening, an impeller in the pump shell is connected with a motor through a pump shaft, the standard thermometer is arranged in the hollow interlayer, and openings are equally distributed on the cavity outer shell. In the invention, the cavity outer shell and the pump are additionally arranged to enable liquid medium in the thermostat to flow in a circulating way in the hollow interlayer, thereby improving the temperature distribution of a black body cavity, enabling the black body cavity to have the characteristic of isothermy and further enhancing the emissivity of the black body cavity.