At present, the highest international benchmark for optical radiation power is cryogenic radiometer, and it can detect radiation covering the vacuum ultraviolet to terahertz spectrum (115 nm~THz). Using the optical and electric alternative principle with the vacuum, low temperature and superconducting technology, it traced the radiation power to the electrical parameters with the high precision measurement, realized super wide spectrum of optical radiation absolute power measurement, the uncertainty reached 10^-5. In the field of national defence military, and optical radiation measurement, photoelectric payload, quantitative remote sensing, high spectral imaging and optical radiation quantity traceability, and others have an irreplaceable role. As the core device of radiation absorption, the cavity of the cryogenic radiometer has a flat spectral absorption with an ultra-high absorption ratio of over 0.999. The absorptance is one of the main factors affecting the high accuracy measurement of the cryogenic radiometer. The scholars at home and abroad have carried out a large number of studies with the theoretical and simulation for the different cavities. However, the experimental measurement and comparison of absorption rates of the cavity with different structural parameters have not been reported. Therefore, to realize the requirement of the wide spectrum and high precision measurement of the radiometer, the research work of developing the cavity suitable for the radiometer has been carried out. We developed four different structures. The wall was 0.1 mm thickness with high conductivity oxygen-free copper (OFHC), the inner surface electroplated nickel-phosphorus (NiP) black coating. The Monte Carlo tracing algorithm was used to simulate the absorptivity of the cavity of four structures. The absorptivity of the cavity was measured by the alternative method, and the measuring device was set up, which was composed of the high stable light source and integrating ball system. By switching the standard whiteboard and the cavity, the absorption rate of the cavity was measured, and the influencing factors of the absorption rate were analyzed. By comparing the simulation and the experimental results, the rationality of the simulation parameter setting is verified. The experimental results show that: (1) comparing the simulation and the experimental result shows, the measurement method and result are verified; (2) the cryogenic radiometer cavity has achieved 0.999 962±0.000 005@632.8 nm; (3) the absorption of the cylindrical cavity with the inclined bottom is better than that of the conical cavity; (4)By designing the screw structure to increase the cavity surface area and the conical aperture to compare with the diaphragm structure, the absorptivity is not significantly increased.