Abstract: Due to the faster dv/dt of high-voltage SiC MOSFET, the common mode interference of its gate driver is more serious. While most existing gate driver power supplies with high isolation voltage usually have the problems of high coupling capacitance, weak common mode transient immunity（CMTI） ability, low conversion efficiency and so on. Therefore, an isolated gate driver power supply with high isolation voltage, high conversion efficiency and low coupling capacitance is designed. Firstly, based on an active clamp flyback converter, this paper proposes a simplified analytical model for coupling capacitance, and the feasibility of analytical model is verified by simulations and experiments. Secondly, the influencing factors and optimization methods of coupling capacitance are analyzed, which provides references for the designs of low coupling capacitance gate driver power supplies. Finally, the performance of proposed high-voltage SiC MOSFET isolated gate driver power supply with low coupling capacitance is evaluated through experiments.The results show that its rated conversion efficiency is about 80%, and power frequency withstand voltage is up to 18 kV. In addition, the coupling capacitance of isolated gate driver power supply is less than 2 pF, so its CMTI capability is extremely strong.