Objective To discuss the effects of elastic modulus on propagation characteristics of ultrasonic guided waves in long bones based on finite-difference time-domain (FDTD) method, so as to provide the theoretical references for evaluating bone fatigue damage at the early stage. Methods A cylinder was used to model the long bone, and FDTD method was used to simulate the long bone with different elastic modulus. Then, the propagation characteristics of different guided wave modes were calculated, including the phase velocity, the group velocity, the central frequency and the energy. Results The elastic modulus of long bones was closely related with the propagation characteristics of ultrasonic guided waves. The phase velocity, the group velocity, the central frequency and the energy were all reduced with the decrease in elastic modulus, and the variation tendency of L(0,5) mode was the most obvious. Conclusions The propagation of ultrasound guided waves can reflect the variation of elastic modulus of long bones, which provides a possible way to evaluate the fatigue damage at the early stage in long bones.