Abstract: Comprehensive Research Facility for Fusion Technology （CRAFT） project is a major national science and technology infrastructure engineer in China. The superconducting magnet research system is one of the main construction and research content of the facility. In order to test the cryogenic performance of full-superconducting magnet,a helium refrigerator with the capacity of 6 kW@4.5 K was proposed and under construction. In the meanwhile, the horizontal vacuum insulated cold box of the helium refrigerator was calculated and verified based on the refrigeration process of helium refrigerator and the dimensions of each equipment of the helium refrigerator cold box, this paper completes the three-dimensional model and structural design of a large horizontal cold box with dimensions of Φ3.8 m×14.5 m. The normal working condition was defined.The relationship between the stress, weight and wall thickness of the cold box under normal operating conditions was analyzed. The wall thickness of the cold box was determined according to the national standard. The stress and deformation of the cold box under normal working conditions were calculated by using the finite element analysis method. The hoisting condition was defined, and the stress and deformation of the cold box under the hoisting condition were calculated. The modal analysis of the cold box was carried out. According to the anti-seismic standard, a group of seismic waves were generated manually. Finally, the seismic response of the cold box shell under combined loads was simulated and calculated using the response spectrum analysis method. The research findings reveal a nonlinear negative correlation between wall thickness and stress-strain, where a thicker wall results in a lesser impact. Under seismic composite loads, the radial deformation of the cold box remains minimal, predominantly exhibiting axial deformation. The structural strength of the horizontal vacuum insulated cold box presented in this article satisfies the requirements for a 6 kW@4.5 K helium refrigerator under various conditions.