Manipulator docking hardware-in-the-loop(HIL) simulation system with the manipulator as a mathematical model will cause instability due to the high contact stiffness of the docking mechanism. To accurately simulate the docking process, the manipulator is equivalent to a six-dimensional spring mechanism during the docking process and the characteristics of HIL system are analyzed. Using root locus method, the influences of HIL system parameters with a mathematical model and a six-dimensional spring mechanism on the stability are compared. Based on the -20 dB/dec crossing frequency theory, the stability criterion, the 3D root locus method and the simulation analysis, the stability and reproduction accuracy are studied from three important aspects of the parameter configuration relation, the system stability condition and the dynamics frequency simulation ability. The experimental results show that when the contact stiffness of the docking mechanism is high, the HIL simulation system with a mathematical model manipulator is unstable but the HIL simulation system with a spring mechanism manipulator is stable; the analysis results obtained from the three aspects which satisfy the stability and reproduction accuracy are consistent with the experimental results. The effectiveness of changing manipulator from a mathematical model to a six-dimensional spring mechanism is illustrated.