The threshold voltage, gate internal resistance, and the gate capacitance are the key electrical parameters of silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs). However, the extraction process is complicated and prone to inaccuracies due to the limited factors such as the parasitic resistance, gate-dielectric interface state in the devices. Therefore, through device modeling and experimental testing, the nonlinear characteristics of gate capacitance of MOSFETs were revealed, and a capacitance-resistance series circuit test method was constructed. Then, the gate internal resistance and threshold voltage characteristics of SiC MOSFETs were studied. The variation law of gate impedance and gate-source voltage, gate capacitance and gate-source voltage were obtained separately in this paper, revealing that when at a gate voltage of -10V, the error between the gate internal resistance and the target value was less than 0.5Ω. Meanwhile, the voltage at the maximum variation of series capacitance with respect to the gate source voltage was approximated as the device threshold voltage. The results were compared with those attained by the constant current method, and verified in SiC planar-gate and trench-gate MOSFETs respectively. Therefore, this capacitance-resistance method provides a relatively convenient method for evaluating and predicting the characteristics of the threshold voltage drift and gate switching oscillations in SiC MOSFET.