The output of the piezoelectric actuators with different external loads was researched by using pure water as the transmission medium at the initial loading pressure of 0.04 MPa (the best load pressure). The results show that the output speed of driver is changed after loading, but the trend of output thrust is invariant. With the load increase, the output speed and thrust are gradually decreased. The driver has the largest output speed of 25.83 mm/s at 350 Hz frequency when there is no load; when the load is 5 N, the maximum output speed is 16.59 mm/s at 400 Hz. At the frequency of 140~260 Hz, the output of step length is approximate a straight line after loading. The maximum bearing value is 30 N at the loading pressure of 0/0.04 MPa; and the maximum bearing value is 20 N at the loading pressure of 0.3 MPa. The maximum bearing value is decreased with the increase of pressure. There is an optimal load to maximize the drive output power, and the proper loading pressure can improve the optimal load values of the driver. The maximum output power of the driver is above 91 mW.