A lownoise, broadband, high dynamicrange underwater acoustic receiver is designed to measure ocean ambient noise. First, new generation true RMStoDC chip AD8436 realizes realtime highprecision calculations of RMS value of the noise signal. Then, microprocessor is used to implement AGC by adjusting the gain code of programmable gain amplifier. Meanwhile, the system gain values are automatically recorded. The receiver has an excellent manmachine interactive interface, through which the gain values are transferred to the embedded host computer online and the system gain can also be set according to customer’s requirement. The experiment result shows that the equivalent input noise of the receiver is lower than 3 μVrms, the frequency band is 20 Hz~5.5 kHz, and the input dynamic range is larger than 68 dB. Besides, the designed receiver is precise, flexible and stable. Therefore, it can satisfy the demand of measurement and analysis of ocean ambient noise.