A high-energy beam additive manufacturing forming device and forming method, comprising a magnetic field unit for assisting additive forming, and further comprising a forming base (6) for placing a material (12) to be processed, and a high-energy beam generation device which emits a high-energy beam, acts on the material (12) to be processed and forms a molten pool (15). The magnetic field unit comprises a first magnetic field generating device (7), and the first magnetic field generating device (7) comprises an induction coil (20) provided below the molten pool (15). The first magnetic field generating device (7) is detachably provided below a surface, used for containing the material (12) to be processed, of the forming base (6); second magnetic field generating devices (16) are provided above the forming base (6); the induction coil (20) is provided below the molten pool (15), and the molten pool (15) is located in an area, where clustered magnetic induction lines are emitted, of the induction coil (20), so that the clustered magnetic induction lines penetrate through the molten pool (15). Therefore, the magnetic field intensity of the molten pool (15) is concentrated, the control effect of the magnetic field on additive forming is improved, and the control efficiency of the magnetic field unit on the molten pool (15) is improved.