Abstract: This paper presents a method to identify the inertial parameters of unknown object handled by the manipulator on a 4-degree-of-freedom(DOF) dual-arm space robot.Based on the conservation principle of linear and angular momentum,the method derives the equations of the mass and mass center as well as inertia tensor of the new end-effector for the manipulator handling the unknown object.These unknown inertial parameters can be obtained from the equations using the linear and angular velocities of the base measured on line when the manipulators move. The feasibility of the method is de-monstrated by the numerical simulation.