Abstract: The method based on the complex two degrees of freedom system(TDFS) mode to design the specification of force-limited vibration testing was proposed. In the method, dynamic sub-structure was adopted to calculate modal effective mass and modal residual mass of specimen structure and supporting structure.The complex TDFS model parameter of vibration system in different frequency bands was defined according to the distribution of mode effective mass in frequency domain.The force spectrum and acceleration spectrum of contact surface between specimen and supporting structure was defined with the excitation condition of supporting structure. Spectrum envelope is the force-limited vibration test profile. Simulation results demonstrate that the force-limited vibration test conditions defined by this method is much more reality on vibration environment than conventional acceleration test condition.