For the identification of mass parameter of noncooperative space target in onorbit servicing missions, a method of mass identification based on vibration characteristic of the flexiblejoint manipulator is proposed. Firstly, the flexiblejoint manipulator captures noncooperative target. Then, the dynamic model of the combinedbody formed by operational spacecraft, flexiblejoint manipulator and noncooperative space target is established. Finally, the mass of noncooperative space target is identified by analyzing the vibration frequency of the manipulator. Numerical simulation results show the effectiveness of the method.