With the development of vibration reduction, noise reduction and noise elimination techniques, the underwater acoustic detection technology tends to extend toward low frequency range gradually. Accordingly, the demand for hydrophones which are suitable for ultra-low frequency band and has high sensitivity becomes more and more urgent. Based on finite element theory, the sensitivity of four types of sound pressure hydrophones is analyzed and compared, and the system model of sound pressure hydrophone with ultra-low frequency and high sensitivity is constructed. By simulation, the modes of first and second order, the admittance curves in air and water and the sound pressure receiving sensitivity are obtained. The results from the simulation show that within the ultra-low frequency band, the sound pressure hydrophone we designed has even frequency response curves in air and water. Based on the simulation, a prototype of sound pressure hydrophone is developed and tested experimentally. The test results indicate that the prototype of sound pressure hydrophone has good ultra-low frequency response character and high receiving sensitivity, which has verified the practicability of the prototype.