Utilizing density functional theory (DFT) calculations, we investigate the influence of the external electric field on the oxygen evolution reaction (OER) performance of monolayer Fe3GeTe2. Monolayer Fe3GeTe2 has ferromagnetic metal properties and displays excellent electrocatalytic activity. The magnetism mainly comes from FeI atoms, owing to the strong Fe-Te orbitals hybridization, and FeI atoms have great effect on the active site Te atoms. The electric field induces the change of spin-electron and promotes charge redistribution in the Fe3GeTe2, resulting in the changes of the magnetic moment and magnetic anisotropic energy (MAE). Simultaneously, the applied electric field shifts the energy band and decreases the work function which facilitates carrier migration to the surface. Therefore, the OER overpotential is reduced and the catalytic performance is improved. These valuable findings can serve as vital references for the design of 2D magnetic electrocatalysts.