A manufacturing method of a trench power semiconductor device is provided. The manufacturing method includes the steps of forming a protective layer on an epitaxial layer and forming a trench gate structure in a trench formed in an epitaxial layer. The trench gate structure includes a shielding electrode, a gate disposed on the shielding electrode and an inter-electrode dielectric layer disposed therebetween. The step of forming the trench gate structure includes forming an insulating layer covering an inner surface of the trench; and before the step of forming the inter-electrode dielectric layer, forming an initial spacing layer, the spacing layer including a first sidewall portion and a second sidewall portion, both of which include bottom end portions spaced apart from each other and extending portions protruding from the protective layer.