The large-caliber steady-state magnetic field testing system is an important device for the International Thermonuclear Experimental Reactor, which is mainly used for electromagnetic compatibility tests in a strong magnetic field environment. Magnetic field performance is the most important parameter of equipment. In the design process, it is necessary to analyze the magnetic field performance and study the influencing factors. This paper mainly studies the axial and radial magnetic fields in the uniform region and the magnetic field characteristics in several typical cases and then analyzes the influence of external ferromagnetic materials and the environmental magnetic field in detail. Finally, an experimental platform is built for a three-dimensional hall test. The results verify the correctness of the analysis.