Evaluation of the receiving voltage sensitivity (RVS) of a hydrophone by using frequency response is investigated for suppressing the RVS estimation error due to the un-correlated noise with transmit and receiving signals. The experiment to estimate the RVS of a hydrophone in a water tank is conducted with a reference projector in the frequency band of 250 to 1000Hz, and the experimental result using frequency response and the conventional method with root mean square (RMS) of the time domain signal are compared. The result with RMS method shows the RVS error occurs in the low frequency range due to the un-correlated noise. However, the result with frequency response shows the RVS error in the low frequency range can be reduced by suppressing the un-correlated noise, so that the flat RVS within 1dB can be obtained in the measured frequency band.