Abstract: The reliable acoustic path (RAP) is an important acoustic channel in deep water. Based on the physical mechanism of RAP and its advantages in detection, the structures of the acoustic rays received in RAP are analyzed by using ray theory. For a 32-element vertical linear array, the variation of the cross-correlations of the received signals with the source range are simulated, and the result shows that a sudden decline of the cross-correlation appears in medium detection range. Based on this phenomenon, the influence of multipath effect on the vertical correlation is studied. It indicates that the time deviation of the acoustic rays with higher amplitude arriving different elements is the main factor to affect the vertical correlation. Finally, some suggestions on the deployment, design and gain analysis of the vertical array in RAP are put forward.