The invention provides a manufacturing method of a shield gate trench power device, which comprises the following steps: providing a substrate with trenches, forming dielectric layers at the bottoms and on the side walls of the trenches, and extending the dielectric layers to the surface of the substrate; filling the trenches with sacrificial layers, wherein the sacrificial layers extend to coverthe dielectric layers on the surface of the substrate; removing the sacrificial layers; and filling the trenches with shielding gate material layers. Before the trenches are filled with the shieldinggate material layers, the trenches are filled with the sacrificial layers, and the closing openings in the top ends of the trenches are weakened or eliminated by etching the sacrificial layers, so that cavities are prevented from occurring in the filling process of the shielding gate material layers, and the electrical property of the device is improved. Further, the sacrificial layers are removedin two steps, after the sacrificial layers are etched to a first preset height position of the trenches in the first step, the exposed dielectric layers are cleaned by a wet method, and under the condition of not influencing the morphology of the lower parts of the trenches, the inclination angles of the openings in the top ends of the trenches are increased, the morphology of the upper parts ofthe trenches is improved, the filling capability of the shielding gate material layers is improved, the cellular density is improved and the device performance is improved.