To design a high-voltage solid-state switch to protect the protect the electron cyclotron tube of J-TEXT Tokamak, the new wide-band-gap semiconductor SiC-MOSFET plays a central role with outstanding electrical characteristics such as low switching loss, high voltage withstand and switch frequency at MHz level. However, the extremely fast switching speed aggravates the switching oscillation, which causes the decreasing quality of the switching waveform when the devices are in straight series. Therefore, it is necessary to develop a precise model to provide guidance for the application of SiC-MOSFET in high-voltage switch. Based on the commercial model developed by CREE, an optimized dynamic characteristic SiC-MOSFET model that can better simulate the influence of nonlinear junction capacitance is proposed. The optimized model comprehensively considers the factors of gate-source voltage and drain-source voltage. A variety of functions are used to reproduce the nonlinear junction capacitance, and the key parasitic parameters such as stray impedance are validated. Through the simulation and 300 V/3 A double pulse test, it is proved that the optimized model has higher accuracy in the change rate of drain-source voltage, change rate of drain-source current, oscillation frequency and turn-off peak voltage. The optimization model is also applied to design the topology of voltage sharing and overvoltage suppression for high-voltage solid-state switch, and the switching module is tested under the condition of 1400 V/700 A. On the key indicators such as turn-off time and peak voltage, the simulation waveform is highly consistent with the experimental waveform. The measured turn-on and turn-off time is less than 120 ns, which meets the design requirements of switching module, and the practicability of the optimization model is reflected.