The invention discloses a manufacturing method of a groove-type double grid MOS structure. The method comprises steps of 1) forming grooves in a silicon substrate by etching; 2) growing a groove layer joint film in the grooves; 3) growing polycrystalline silicon in the grooves, and performing reverse etching to form source polycrystalline silicon; 4) removing a part of the groove layer joint film, and enabling the height of the groove layer joint film to be lower than that of the source polycrystalline silicon; 5) growing a thin oxide layer of the thickness of 200-400 Angstrom; 6) depositing silicon nitride; 7) growing grid polycrystalline silicon and performing reverse etching to the substrate surface; and 8) performing base injection and source injection, depositing an inter-layer dielectric layer, etching contact holes, manufacturing metal and passivation layers and finishing manufacturing of the device. The method improves the quality of the gate oxide and the pressure-resistance property and the reliability of the device by optimizing the membranous structure of the gate oxide and the dielectric layer and through the combination of the thin gate oxygen + silicon nitride, thereby satisfying the leakage requirements between the two layers of polycrystalline silicon.