A parameter identification method based on test data was proposed to evaluate the nonlinear stiffness of a tail drive shaft system. Firstly， modal testing on the tail drive shaft system under low-amplitude excitation was carried out， and a simplified dynamic model of the tail drive shaft system was established， which was verified by testing results. Then， the stepping sine sweep testing under different excitation levels was conducted， and the relationship between natural frequency and displacement amplitude was obtained based on the measured frequency response function. Moreover， the finite element iterative calculation of the simplified model was carried out to achieve the relationship between the natural frequency and the equivalent stiffness of the tail drive shaft system. Finally， the relationship between the equivalent stiffness and the displacement amplitude was established， and the nonlinear stiffness of the tail drive shaft system was identified.