Electrical devices (thyristor and fuse) is a key element of superconductor magnet high power AC/DC converter and their performance are the reliable guarantee for the converter. In this paper, the worst current surge that is the most important factor of electrical device selection confirmed by the short circuit fault of converter, First. Secondly, the steady and transient junction temperature are simulated of three kinds of thyristors by MATLAB and PSCAD based on the rated condition and short circuit fault condition to determine the thyristor type and parallel number. Then, the fuse type is selected to match the selected thyristor by overcurrent and overvoltage analysis. Lastly, both of the reliability of the selected thyristor and fuse are verified by surge current I2t analysis.