In order to meet the needs of sound pressure detection in complex underwater environment in many fields, a capacitive sound pressure hydrophone based on MEMS is proposed. The design of oil injection hole and oil injection channel is developed. The sensor is encapsulated in silicon oil. By balancing the internal and external pressure of vibration film, its ability of withstanding static water pressure can be improved. The hydrophone was modeled through Comsol Multiphysics simulation software, and the static analysis, modal analysis and sensitivity analysis under harmonic acoustic signal disturbance were carried out by utilizing the thermosviscous acousticstructure multiphysics field. The influences of thermal effect and viscous effect on small size acoustic transducer are considered in finite element analysis, which makes the simulation results more convincing. The receiving sensitivity of the hydrophone is -147 dB under the disturbance of the harmonic acoustic signal with the amplitude of 10 Pa and frequency of 1 Hz~10 kHz. The simulation results show that the designed capacitive acoustic pressure hydrophone has the characteristics of high sensitivity and wide band, which could meet the measurement requirements of underwater low frequency acoustic pressure signals in different fields.