The active vibration isolation system of helicopter is established by using piezoelectric stack actuators installed on struts of main gearbox. Based on the constitutive relation of piezoelectric materials, the driving equation of the piezoelectric stack actuator is deduced, and the dynamic model of the main gearbox vibration isolation system driven by the piezoelectric stack actuators is established. The adaptive filtering process is realized by the least mean square(LMS) algorithm. The active vibration isolation simulation of helicopter is carried out, indicating that the system has an effective vibration isolation effect.