A magnetic field-assisted vibratory finishing device for a minute structure and a finishing method is provided. The device includes a rotating shaft, a workpiece clamping device, a magnetic field generating device, a vibration assisting device, a three-axis precision displacement platform and a base. The magnetic field generating device includes a baffle plate, magnetic bars and a magnetic-pole groove. The vibration assisting device includes a housing, guide fixing rods, a vibration motor, a vibration connecting plate, and compression springs. The workpiece clamping device clamps parts with a variety of structural shapes, and a frequency controller can control the motion mode of the magnetic field generating device during the finishing processing, thereby controlling the motion track of grinding material.