Abstract: Even without eyesight and hearing, harbor seal can identify and track the wake of swimming fish in the water by its whiskers with a special shape. From the biomimetic point of view, study on the vibration responses and the tracking mechanisms of harbor seal whisker in wake flow contributes to the development of a new-type underwater sensor. In this paper, direct numerical simulation of the vortex-induced vibration of the harbor seal whisker in uniform and wake flow with a Reynolds number of Re=300 and a reduced velocity of U_\rm r=6.0 was performed by applying the iterative immersed boundary method. The vibration characteristics and the wake structures of the whisker models are investigated and compared with those of a circular cylinder and an elliptical cylinder with the same equivalent diameter. The effects of different structural shapes on the vibration characteristics and wake structures are analyzed, and the sensing ability and tracking mechanisms of the harbor seal whisker are discussed. The simulation results show that the whisker model can significantly reduce the drag force and suppress the vibration responses in uniform flow. It undergoes a chaos motion with a very low amplitude, which provides a pure signal background for harbor seal's whisker for sensoring. However, in wake flow, the vibration response of the whisker model increases significantly, being stable and periodic. As a result, the whisker model has a higher signal-to-noise ratio and sensitivity than other cylinders. This reveals the mechanism of harbor seal using its whiskers to identify and track the wake of swimming fish in the water, which is of great significance for the development of a new-type underwater detector.