Thickness vibration mode is commonly used for high-frequency transducers. For disc piezoelectric ceramics, there is no ideally pure thickness vibration mode because the coupling between the radial and thickness modes always exists. Furthermore, it also deteriorates the transmission voltage response and directivity of the high-frequency transducer. In this paper, based on the theoretical calculation and finite element simulation method, a new method was proposed, and the related experiment was carried out to convince this idea. Both the simulation analysis and experimental results show that drilling a hole at the center of piezoelectric vibration is a simple but effective method to obtain a pure thickness vibration mode of the disc piezoelectric ceramic, and then improve the transmitting ability and directivity of the high-frequency piezoelectric transducer. The sidelobe level is as low as −21.3 dB.