The waveguide invariant is used to describe the relationship between the slope of interference fringes, the frequency and the distance of the source in the frequency-distance acoustic intensity diagram. The waveguide invariant method considers the influence of the channel environment on sound propagation and reduces the dependence on environmental parameters, which makes its robustness stronger. In this paper, the ranging algorithm using a single element is discussed without considering the information of waveguide environment parameters. Based on the horizontal hydrophone array, the array signal processing method is used to improve the accuracy of ranging compared to a single element. The experimental results show that the ranging accuracy of this method is improved to less than 2% at a long distance after the conventional beamforming (CBF) processing. The above results show that the array signal processing method used improves the accuracy of the distance measurement obviously.