The invention relates to a gate self-alignment type silicon carbide MOSFET and a preparation method therefor. According to the preparation method, the gate self-alignment type silicon carbide MOSFET is prepared by taking polycrystal silicon carbide as a self-alignment gate electrode precursor of the silicon carbide MOSFET; in the preparation process, the polycrystal silicon carbide replaces polysilicon to be used as a gate self-alignment ion injection mask, so that the preparation of the silicon carbide MOSFET can fully execute a gate self-alignment process in a silicon MISFET manufacturing process; and therefore, the problems of metal pollution and low alignment precision of the existing channel self-alignment process can be solved.