Voltage control of magnetic properties is a promising path to realize low-power spintronic devices and meets the requirements for quicker information processing speed and ongoing scale reduction. Hydrogen migration induced by voltage gating has been demonstrated to modify the intrinsic magnetic properties of materials by affecting the exchange interaction, electron occupancy, and magnetoelastic effect. Herein, the magnetic properties of a ferrimagnetic Gd29Fe71 film in an all-solid-state multilayer device, which is constructed using a GdOx electrolyte, can be reversibly modulated by voltage-controlled hydrogen migration. Polar MOKE results indicate that hydrogen intercalation/deintercalation can modulate the Gd29Fe71 film's degree of compensation and control the dominant magnetic sublattice. Furthermore, the polarity of the polar MOKE curves can be reversibly switched. As with the increase in hydrogen loading, the compensation point in the Gd29Fe71 film is approached, the density of magnetic domain nucleation sites decreases, and the magnetic domain structures transform from labyrinth domains to uniform large area domains. At the same time, a strong perpendicular magnetic anisotropy is developed. This work shows a possible pathway for reversible control of magnetism in spintronic devices.