Single-point incremental forming (SPIF) has drawn much attention recently due to its flexibility in making parts for rapid prototypes and small samples. Several studies have pointed out the benefits of using ultrasonic vibration (UV) in SPIF experimentally. This study verifies the effect of UV in reducing the forming forces by performing numerical simulations. In addition, the effect of several process parameters, including tool diameters, rotational speeds, step sizes, and ultrasonic vibration amplitudes, is investigated in detail. It is found that an increase in the tool rotational speed and vibrating amplitude decreases forming forces, whereas an increase in the vertical step size increases forming forces.