A new finish process that uses a rotational magnetic-assistance with high efficiency to assist discharging dregs out of the electrodes’ gap during the ultrasonic electrochemical finishing on the freeform-surfaces is investigated in the current study. The factors affecting the effects of the magnetic-assistance in ultrasonic electrochemical finishing are primarily discussed. The mainly experimental parameters are rotational speed of the magnetic-assistance mechanism, magnetic strength, distance between the two magnets, current density, and frequency and power level of ultrasonics. A large rotational speed of the magnetic-assistance mechanism produces a better finish. Providing large magnetic field intensity or using a small distance between the two magnets produces a larger magnetic force and discharge ability, and a better finish. A higher current density with magnetic-assistance reduces the finish time and avoids the difficulty of dreg discharge. The rotational magnetic-assistance during the ultrasonic electrochemical finishing process makes a great contribution in a short time by making the freeform-surfaces of workpiece smooth and bright.