A novel asymmetrical inertial piezoelectric rotary actuator with a bias unit was proposed for improving the output performance of inertial piezoelectric actuators. On the asymmetrical clamp, the bias unit was designed. To research the effect of the bias unit on the output performance of piezoelectric rotary actuator, a mechanical model equation of the mechanism was initially established, and the dynamic characteristics of the actuator were also derived and simulated. Then, a prototype was designed and fabricated, corresponding experimental system was built to conduct experiments and experimental results were compared with that of the actuator without the bias unit. The results show that the output angular velocity peak of the actuator is at the offset distance of 15 mm. Compared with the actuator without the bias unit under the driving voltage of 100 V, 23 Hz, the actuator with the offset distance of 15 mm improves the maximum angular velocity from 3.48 rad/s to 5.39 rad/s, enhancing by 54.88% and the highest driving moment from 2.41 N·mm to 3.62 N·mm, enhancing by 50.2%. In addition, its heavy bearing capacity at stable motion attains 1 300 g under the driving voltage of 100 V, 4 Hz. Both theoretical and experimental results indicate that the designed actuator hold advantages in larger angular velocities and inertial driving moments in comparison to the one without the bias unit.