Abstract: In order to test the superconducting magnet performance for the Comprehensive Research Facility for Fusion Technology (CRAFT) project of China, a power supply converter needs to be designed. In this paper, short circuits upstream and downstream of the direct current (DC) reactor are analyzed, and the thyristor style and the parallel number are determined by the limit analysis of junction temperature and fault current I²t. On this basis, the over current and voltage verification of fast fuse are finished to protect the thyristor at fault cases by considering the short circuit of the bridge arm. Then, the resistor and capacitor parameters of thyristor snubber are committed to decreasing the reverse over voltage. These analysis results will be used as the preliminary design of high power magnet converter for CRAFT.