This paper studies the influence of parasitic inductance on overvoltage of medium voltage DC solid state circuit breaker (SSCB) based on the normally-on silicon carbide (SiC) junction field effect transistor (JFET) series structure, and proposes an overvoltage suppression method for SSCB on this basis. Firstly, the topology and operation principle of the SSCB based on the series structure of the normally-on type SiC JFETs are introduced, and the mathematical model of the switching process for the SiC JFET series structure considering the parasitic inductance of the complete loop is established. Secondly, MATLAB software is used to analytically calculates the mathematical model, and the mechanism of overvoltage generated by parasitic inductance during SSCB switching to SiC JFET devices in series operation is revealed. At the same time, the simulation results of PSPICE verify the correctness of the theoretical analysis. Finally, single gate drive and snubber circuit are designed for SSCB overvoltage suppression, and the SSCB experimental prototype verifies the effectiveness of the proposed method.