Aiming at the problems that the single-shot and single-acquisition water-acoustic ranging method in the shallow sea environment has high computational complexity and is susceptible to the special underwater environment, a low-complexity ranging method suitable for underwater acoustic multipath channels is proposed. Firstly, the composite code is applied to the underwater acoustic positioning system as a synchronous ranging signal, which supports fast and accurate signal synchronization and multipath delay detection. Then, an improved weighting function generalized cross correlation (GCC) algorithm is proposed to extract the multipath delay. Finally, a matching function is introduced to multiply the multipath delay. The path delay is correctly matched to the propagation path, and the geometrical methods such as hyperbola and triangle are used to calculate the distance between the transmitting and receiving ends. Simulation results show that in multipath and low signal-to-noise ratio ( - 10 dB) environments, the synchronization accuracy of the composite code is 100% and the computational complexity is low. Compared with the phase transformation-generalized cross correlation (PHAT-GCC) algorithm, the multipath of the GCC algorithm with an improved weighting function is improved. The delay detection performance is improved by nearly 6 dB, and based on this, a single receiving node can achieve ranging of underwater targets.