Abstract: Nonlinear physical parameters of the docking mechanism-inertial,damping and stiffness matrices,are identified by direct parameter estimate(DPE)method with input-output data of the system.First,a simplified nonlinear dynamic equation with physical parameters is established.Then the equation is transformed to a parameter-linear identification model,which considers the null-element distribution and the symmetric property information of the parameter matrices of the system.DPE method that requires synchronously measured displacement,velocity and acceleration data and 4-order difference DPE method that only needs displacement data are employed to identify the physical parameters of the docking mechanism respectively.Finally,the feasibility of the methods is verified with a 6-DOF model of the docking mechanism.