In order to meet the working requirements of low-frequency piezoelectric hydrophones, to address the self-noise optimization problem of piezoelectric hydrophones with pre-amplifiers, the equivalent noise model of two-port network is theoretically derived, and the SPICE model is established using LTSPIC to simulate the noise of key components. The low noise amplifier circuit is designed and manufactured based on the junction field effect transistor. The self-noise test on the designed amplifier and the hydrophone with pre-amplifier shows that the equivalent input noise of the amplifier is 8.48 nV/Hz@1 kHz, and the inflection point of 1/f noise is about 350 Hz, which is better than that of the existing integrated operational amplifier; the noise spectrum level of the hydrophone with pre-amplifier is 33.577 dB @1 kHz, which is lower than the zero-order sea state noise spectrum.