Under the actual marine environment, the underwater ultrasonic measurement system has a certain limitation because of mechanical noises such as background noise and reverberation noise. The bispectrum time delay estimation method with Gaussian noise has shielding capacity and is capable of suppressing noise. This method adopts an accurate estimation of the signal time delay, and its power spectral bispectrum reconstruction is superior to the direct use of FFT transform power spectrum estimation, thus having relatively high precision and performance. In view of underwater ultrasonic detection deficiencies, the bispectrum estimation method is adopted due to its insensitivity to background noise. According to measured data obtained in laboratory pool, the applicability of the method is verified. The results show that the bispectrum method has better applicability than the cross-correlation method under the conditions of less prior knowledge and strong background noise.