The invention provides a SiC MOSFET power device and a preparation method thereof. The device comprises a substrate, an epitaxial layer, a trench, a gate dielectric layer, a gate conductive layer, a well region, a source region, a body contact region, an SBD diode region, a front metal layer and a drain metal layer, wherein the epitaxial layer is positioned on the surface of the substrate; the trench is located in the epitaxial layer, and the upper opening of the trench is larger than the lower opening of the trench; the gate dielectric layer is positioned on the side wall and the bottom surface of the trench; the gate conductive layer is located on the surface of the gate dielectric layer and fills the trench; the well region is located in the epitaxial layer and is located on the periphery of the trench; the source region is located in the well region; the body contact region is located in the well region; the SBD diode region is located in the epitaxial layer. According to the device, the structure of a traditional SiC MOSFET power device is optimized, so that the conduction resistance and the conduction power consumption of the device can be reduced, and the device can also have a relatively low input capacitance, the switch speed of the device is increased, the power consumption of the switch is reduced, the reverse conducting capability of the device is improved, and theoverall size and the economic cost of the power module are reduced. The structure and the method are simple, and a wide application prospect is achieved.