Abstract: The undulated bottom in shallow water has a significant effect on sound propagation. Based on the summer hydrological data in the East China Sea, the sound field characteristics in long-distance undulated bottom environment with random bottom roughness are analyzed by using the Monte Carlo method, and the range-dependent propagation mechanism is analyzed by using the ray model. Numerical simulations indicate that the high-frequency sound wave is more sensitive to the bottom roughness, and the probability distribution of transmission loss (TL) is more dispersed. In the negative thermocline environment, when the source locates below the thermocline, the effect of undulated bottom on sound propagation is more significant for the receiver located below the thermocline. In the isothermal environment, the undulated bottom has less influence on sound propagation than in the thermocline environment. And, the greater the inclination of the undulating seabed, the greater the acoustic transmission loss will be. For the same inclination, the relative undulation, namely the ratio of undulated height to water depth, has the greater influence on sound propagation than the change in the length of an undulation cycle.