Abstract: The cyclotron built in China Institute of Atomic Energy is a high current and compact proton cyclotron with extracted beam of 75-100 MeV and designed current of 200 μA. The center region and spiral deflector installed in the narrow gap of the cyclotron are the key parts in this cyclotron. The structure design is affected by magnetic field, RF field, high voltage electric field, vacuum and heat dissipation. In this paper, the structure design and application were introduced. To solve the reliability problem of the center region and spiral deflector with high current beam injection, the insulation distance increased, the RF connection structure was optimized, and the apertures were put in front of the deflector in the design process. The heat dissipation of the spiral deflector was analyzed, and the temperature distribution of the spiral deflector with high beam current was obtained. The designed center region and spiral deflector were installed in the 100 MeV cyclotron. The cyclotron was tested for 20 μA/100 MeV for 12 h. The center region and spiral deflector work stably in the test.