The high-speed motor of underwater vehicle has the characteristics of high-speed, high-power and multi-gear adjustable, etc. In order to reduce the torque ripple of high-speed brushless direct current motor (BLDCM) in the limited space of underwater vehicle, the demand for high switching frequency of high-speed motor of underwater vehicle is analyzed. The torque ripple of BLDCM is analyzed mathematically, so the relationship between torque ripple and switching frequency and duty ratio of BLDCM is obtained. The high switching frequency of SiC MOSFET is used to improve the switching frequency of inverter and reduce the torque ripple of highspeed motor. At the same time, SiC MOSFET has the advantage of low switching loss. Therefore, compared with insulated gate bipolar transistor (IGBT), SiC MOSFET can reduce the system efficiency caused by switching loss while improving the switching frequency. Finally，the effect of SiC MOSFET on torque ripple suppression of highspeed BLDCM at higher switching frequency is verified by simulation and experiment, which provides a reference for the application of widebandgap semiconductor devices in highspeed BLDCM of underwater vehicles.