Sandwich transducers are extremely versatile, but when the lateral dimension is too large, the displacement of the radiating surface is uneven due to the coupling vibration. Due to the unique vibrational band gap characteristics of phononic crystal, vibrations in the bandgap range can be prohibited from propagating for infinite periodic structure or suppressed for finite periodic structure, which makes it widely used in the field of vibration suppression. In this paper, a two-dimensional phononic crystal structure is formed by processing periodically aligned grooves in the front cover of a large-sized sandwich transducer. Since the periodic grooves are formed in the radial direction, the radial waves cannot propagate, and thus the lateral vibration is suppressed. Subsequently, the finite element method is used to simulate the vibration transmission characteristic, resonance frequency and emission voltage response of a large-sized sandwich transducer based on two-dimensional phononic crystal. The effects of slot height and slot width on its bandgap, resonance and anti-resonant frequency, bandwidth, and displacement profile of the radiating surface are discussed. The results show that the phonon crystal structure can be optimized by using a large-sized sandwich transducer. The large-sized sandwich transducer based on two-dimensional phononic crystal has a lateral band gap. When the operating frequency of the large-sized sandwich transducer is within the band gap range, the two-dimensional phononic crystal structure can effectively suppress the lateral vibration, and the uniformity of the displacement distribution of the radiating surface of the transducer is improved. In addition, when the slot width is constant, the bandwidth of the large-sized sandwich transducer based on the two-dimensional phononic crystal increases as the slot height increases. Similarly, when the slot height is constant, the bandwidth of the large-sized sandwich transducer based on the two-dimensional phononic crystal increases as the slot width increases. The two-dimensional phononic crystal structure is processed in the front cover of the large-sized sandwich transducer, and the working frequency band of the large-sized sandwich transducer is effectively broadened.