The clinically used middle-ear implant for round-window stimulation is not designed specifically for this excitation method, and there are problems such as large individual differences in postoperative performance, unstable performance, and gain value that cannot reach the theoretical value. To address these issues, a round-window stimulating type piezoelectric actuator that matches the size of the round-window membrane and can monitor the preload acting on the round-window membrane is designed. Firstly, combined with the anatomical structure of the human ear, the mechanical structure and macroscopic dimensions of the actuator are designed. Then, the force analysis of the flextensional amplifier is carried out, and the particle swarm algorithm is used to optimize the design of the flextensional amplifier to obtain the optimal output displacement magnification. After that, a piezoelectric actuator-human ear coupling mechanics model is formulated, the influence of the cross-sectional area of the support spring and the number of piezoelectric stack layers on the performance of the actuator′s hearing loss compensation is analyzed, and the cross-sectional area of the support spring and the number of piezoelectric stack layers are ascertained. Finally, the prototype of the piezoelectric actuator is manufactured according to the determined design size. A laser vibration test bench is established to test the dynamic characteristics of the piezoelectric actuator. The experimental results show that the designed round-window stimulating type piezoelectric actuator can monitor the preload acting on the round-window membrane. It has the advantages of wide operating frequency band (100~ 10 000 Hz) and low harmonic distortion (THD ≤0. 29% ). The designed piezoelectric actuator is suitable for the hearing loss compensation of the round-window stimulation, which provides a new solution for the clinical treatment of mixed hearing loss.