A superconducting multi-coil magnet system has been designed, analyzed and optimized, serving as demonstrator for a high filed Magnetic Resonance Imaging (MRI). The designed superconducting magnet inductance is 3500H. The operating current is 230A. The stored energy is as high as 93MJ. The superconducting material is NiTi/Cu. The normal excitation and demagnetization are completed by the power supply, after the excitation, the power supply is disconnected. This paper presents the design and research of the two different kinds of magnet power supplies which are all adjusted for the project, the one is three-phase bridge phase-controlled rectifier which is simpler and the other is based on high-frequency which is of high power density, reduced weight, and low noise without compromising efficiency and reliability. Besides, the design of the quench detection systems for solenoid model coil was also described in this paper.