The output performance of stick-slip piezoelectric actuators is comprehensively determined by the electro-mechanical responses of the driving unit, control strategy, and the contact status between the driving unit and the slider. Most previously developed inertial piezoelectric actuators face the problems of frequency dependence, motion speed, excessive volume, step resolution, and loading capacity. To exhaustively improve actuation performance, we propose a compact bi-directional piezoelectric-based rotary actuator incorporating the single excitation source, rhombic amplification mechanism, and adjustable preload. The numerical simulations are implemented based on the LuGre friction model, to guide the system optimization. A prototype is fabricated and examined, which accomplishes the maximum load torques of 27.78 and 30.87 N.mm in clockwise and anticlockwise directions, respectively, at the highest rotational velocity of 0.4720 rad/s. Compared with previously reported inertial actuators, the performance of the proposed actuator is significantly enhanced, promising in applications requiring nanometer resolution, long stroke, large holding, and driving forces.