Abstract: The acoustic absorption of water is negligible in short-distance low-frequency sound propagation. However, in the actual propagation process, the propagation distance may reach hundreds or even thousands of kilometers. At this time, seawater absorption will have a great impact on the sound field. In this case, significant errors are induced in the long-distance sound field calculation results if the acoustic computation model does not take the acoustic absorption of water into account. The sound fields in ideal total reflection waveguides and in the deep-water environment with Munk sound speed profile are calculated by using several different models to illustrate the effects of the acoustic absorption of water on long-distance sound field calculation. Then, the acoustic absorption of water is added in the RAM model to make it more accurate for the computation of long-distance underwater sound propagation. The results of numerical examples show that the transmission loss obtained by the improved RAM model is consistent with the results given by COUPLE model and SCOOTER model. Therefore, it is confirmed that using the improved RAM model incorporated with the acoustic absorption of water to solve long-distance sound propagation problem is correct and feasible.