Abstract: Ray mode is a classical propagation mode in underwater acoustics,which can be calculated rapidly and has a clear physical meaning.The power carried by each ray tube is conserved,which "flows" along the ray tube and does not cross the ray tube wall.Once the ray tubes′ propagation rule is known,the specific power distribution in the ocean can be determined.Based on the Harpo mode,the ray tube trace is calculated and propagation characteristics in the typical seabed terrain analyzed.Simulation results show that the seabed terrain has a strong effect on the ray tube trace,resulting in an obvious excursion in the plane direction and causing significant errors in sonar detection and location.