The invention discloses a method for manufacturing a trench gate MOSFET with a shielding grid, and the method comprises the steps: providing a semiconductor substrate and carrying out the photoetching of the semiconductor substrate to form a trench; carrying out the growth of a first insulating layer; carrying out the back etching of the first insulating layer; carrying out the angle etching of the first insulating layer to form a bottom insulating layer, and enabling the thickness of the bottom insulating layer to be gradually increased from the top to the bottom; carrying out the depositing of a first polycrystalline silicon layer, and carrying out back etching to form a polycrystalline silicon shielding grid; forming a polycrystalline silicon isolation dielectric layer; forming a gate medium layer; carrying out the depositing of the second polycrystalline silicon layer, and carrying out back etching to form a polycrystalline silicon shielding grid. The method can form the bottom insulating layer with continuously changing thickness at the bottom of the shielding grid, is simple in technology, is low in cost, can further improve the breakdown voltage, and achieves a better specific on-resistance.