The pillar plate phononic crystal (PC) structure is benefit for the mass loading and liquid detection. A pillar plate phononic crystal point defect is proposed and fabricated in this paper. The band gap calculation is carried out by using the finite element method and the vibration mode of the point defect mode of the phononic crystal is simulated. An AlN acoustic wave sensor based on silicon is fabricated by MEMS processing. The performance of the selected point defect mode is tested and analyzed through the mode selection of the electrode configuration. The results show that the point defect mode with relative high frequency can be obtained through reasonably designing the electrode. In the experiment, the mode frequency of selective incentive is 7.732 MHz and the corresponding Q value is 700 in the air. This provides a theoretical and experimental basis for realizing the liquid phase detection.