Irradiation testing is an essential phase in the qualification process for new materials designed for nuclear reactor applications, which evaluating the ability of these materials to retain their performance in the real condition. The temperature of the test specimen is a crucial parameter during irradiation testing, however the heat release rate along the axial direction of the test section is typically non-uniform as the result of the attenuation of gamma rays, leading a cosine temperature distribution from the center to the ends. That is because the nuclear reaction intensity in the reactor is cosine function distribution along the axial direction, so the gamma intensity emitted by the nuclear reaction is also a cosine function distribution. Irradiation test section and the fuel element are parallel to each other, and gamma rays of different intensities attenuates as it passes through the material, leading a cosine temperature distribution from the center to the ends. To minimize the axial temperature gradient, a new design of irradiation facility with heat pipes is proposed in this paper to achieve a more uniform temperature distribution along the specimen during irradiation tests. Computational Fluid Dynamics (CFD) are employed to verify its feasibility and uniform ability of temperature. A geometric model configured with heat pipes was developed, research adjusts various parameters, and the influence of various structural parameters on temperature profiles are investigated numerically, including the number of heat pipes, the length of the evaporation section, the radial distance from the specimen, the outer diameter, and the wall temperature of the heat pipes. The findings indicate that the integration of heat pipes in the test section can markedly influence the temperature distribution of the irradiated specimen. By adding 2 heat pipes, adjusting length slightly shorter than test section and adjust other parameters, it is possible to control the temperature profile of the specimen. The maximum temperature difference in the test section without heaters is about 18 °C, while the maximum temperature difference with heaters is <10 °C. This study highlights the importance of heat pipe optimization in enhancing the accuracy of irradiation testing for new nuclear materials.