To improve mechanical output performances of the sandwich piezoelectric actuated tracked mobile system, a U-shaped preload adjusting mechanism is proposed, and experimental investigations on the relationship between the preload and the output performance of the sandwich piezoelectric actuated track mobile system are carried out in this study. At first, finite element simulation analysis is conducted to study the influence of the installation of the U-shaped preload adjusting mechanism on the vibration characteristic of the sandwich piezoelectric actuator. Additionally, the optimal preload force corresponding to the maximum traction force of the sandwich piezoelectric actuated tracked mobile system prototype with the installation of the U-shaped preload adjusting mechanism is experimentally determined. Finally, traction characteristics, obstacle crossing performances, and motion characteristics in the simulated lunar soil environment are experimented for the tracked mobile system prototype under the optimal preload force state. Experimental results indicate that the mechanical output performance of the sandwich piezoelectric actuated tracked mobile system is improved when it worked in the optimal preload force state. These provide the technology support and experimental basis for the future application of the piezoelectric actuated tracked mobile system on lunar rovers.