A method of manufacturing a grooved-gate MOSFET device based on a two-step microwave plasma oxidation, including: etching a grooved gate, and oxidizing silicon carbide on a surface of the grooved gate to silicon dioxide by microwave plasma to form a grooved-gate oxide layer, the step of forming the grooved-gate oxide layer including: placing a silicon carbide substrate subjected to the grooved gate etching in a microwave plasma generating device; introducing a first oxygen-containing gas, heating generated oxygen plasma to a first temperature at a first heating rate, and performing low-temperature plasma oxidation at the first temperature and a first pressure; heating the oxygen plasma to a second temperature at a second heating rate, introducing a second oxygen-containing gas, and performing high-temperature plasma oxidation at the second temperature and a second pressure until a predetermined thickness of silicon dioxide is formed; stopping introduction of the oxygen-containing gas, and completing the reaction.