A manufacturing method for a semiconductor device with a discrete field oxide structure is provided, the method includes: growing a first PAD oxide layer on the surface of a wafer; forming a first silicon nitride layer (302) on the first PAD oxide layer through deposition; defining a field region by photolithography and etching same to remove the first silicon nitride layer (302) located on the field region; performing an ion implantation process to the field region; performing field region oxidation to grow a field oxide layer (304); peeling off the first silicon nitride layer (302); wet-dipping the wafer to remove the first PAD oxide layer and a part of field oxide layer (304); growing a second PAD oxide layer on the surface of the wafer, and forming a second silicon nitride layer (312) on the second PAD oxide layer through deposition; defining a drift region by photolithography and etching same to remove the second silicon nitride layer (312) on the drift region; performing an ion implantation process to the drift region; and performing drift region oxidation to grow a drift region oxide layer (314). The above-mentioned method peels off the silicon nitride layer (302) after the growth of the field oxide layer (304) is finished, at this time, the length of a bird beak of field-oxide (304) can be optimized by adjusting a wet-dipping amount to solve the problem that the bird beak of field-oxide (304) is too long.