Due to the demand of controlling magnetism by electric fields for future storage devices, materials with magnetoelectric coupling are of great interests. Based on first-principles calculations, we study the electronic and magnetic properties of a double perovskite Sr2CoMoO6 (SCMO) in a hybrid heterostructure combined with BaTiO3 (BTO) in different polarization states. The calculations show that by introducing ferroelectric state in BTO, SCMO transforms from an antiferromagnetic semiconductor to a half-metal. Specially, altering the polarization direction not only controls the interfacial magnetic moment, but also changes the orbital occupancy of the Co-3d state. This novel multiple magnetoelectric coupling opens possibilities for designing new type of spintronic and microelectronic devices with controllable degree of freedom of interfacial electrons in the heterostructures.