Abstract: Ultrasonic Lamb wave method is a common method to detect the damage of fiber reinforced plastics (FRP) plate. However, the anisotropy material property of FRP will have a great effect on the accuracy of damage location based on lamb wave method. In order to solve this problem, a time probability density method was proposed. The method is developed from traditional ellipse method and it considers the anisotropy property of FRP material. By taking account of the group velocity variation of A₀ mode waves with different propagation directions, this method calculated the travel time of the reflection wave with any damage on FRP plate, and the time flight diagram could be obtained. By establishing the mapping relationship between the time of flight and the travel time of the actual damage reflected wave, a time probability density map could be obtained to characterize the probability of the existence of the damage. The result from numerical analysis and experimental study shows that the damage location error of this method can be reduced by more than 70% compared with that of the traditional ellipse method. This paper demonstrates the feasibility and accuracy of this method for the damage location of anisotropic FRP plates.