Abstract: In the preparation process of novel polymer quartz piezoelectric sensors using AT-cut quartz substrates and polymer materials, the roughness and the chemical characteristics of the substrate surface have a great influence on the production of the sensors. It could result in thickness-varied or defective films of the sensors, which make the sensor's frequency signals unstable. In this paper, a mechanical model of the sensor is presented, which takes into account the conditions that the film is thickness-varied and defective. The ANSYS software was used to obtain the vibration characteristics of the mechanical model under complex conditions by modal analysis. Results show that the natural frequency values of the sensor change from a stable state to a divergence state with the increase of the film defect in the radius, and the natural frequency values of the sensor increase linearly with increase of the thickness for the film. It indicates that the thickness of the film should be kept uniform and the defect radius should be limited within 0.5 mm during producing the sensors. The results provide an important basis for producing the qualified polymer quartz piezoelectric sensors.