The invention discloses detaching and mounting methods for a braking air damper of a hydraulic generator. The two methods both use a detaching device, the detaching device comprises a support frame, a lifting frame, a pushing table, a first hand-pull hoist and a second hand-pull hoist, wherein the support frame plays a role of integral supporting, the first hand-pull hoist controls the lifting frame to be lifted, and further the pushing table and the braking air damper are driven to be lifted. Therefore, the problem of difficulty in hoisting of the current braking air damper is effectively solved, manpower, material resources and time are saved, and the detaching and mounting efficiency is effectively improved.