The threedimensional model of CMUT unit was established to study the effects of different structures of CMUT unit on the performance of CMUT and the CMUT structure parameters was obtained. The operating frequency range of 1~2 MHz and working voltage of Vdc<100 V were set. First, the membrane parameters were determined by using the finite element model for the modal analysis to study the relationship between the membrane parameters and first order frequency. Then, the effect of the gap on the performance of CMUT was simulated and analyzed based on the explanation theories and static analysis and the gap thickness was determined. Finally, the electrode parameters were optimized through the electrostatic  mechanical coupling analysis and the calculation of the electromechanical coupling coefficient. The simulation verification of the proposed CMUT structure was carried out through COMSOL Multiphysics. The result showed that the working frequency was 1.65 MHz and collapse voltage was 68 V, which met the requirements of design.