The capacitive micromachined ultrasonic transducer (CMUT) made by MEMS technology has the advantages of wide frequency band, easy integration with electronic circuits, and broad application prospects in the field of medical imaging. In order to study the characteristics of acoustic field emitted by a close-packed CMUT, a simple physical domain interaction analysis method is proposed in this paper. Based on the vibration theory of thin plate, the analytical solution of the radiation sound field of CMUT element is obtained by the calculation from the acoustic radiation principle and characteristics of CMUT cell. The correctness of the first-order vibration mode equation based on the thin plate vibration theory is verified by the vibration distribution experiment of diaphragm. Through simulation and experiment, the acoustic field distribution, axial sound pressure and directivity of CMUT transmitter units under different arrangement modes and conditions are studied, which provides theoretical basis for the design and performance analysis of CMUT.