In order to study the influence of non-linear factors on skid helicopter ground resonance， a concise and effective equivalent planar model of helicopter ground resonance is established based on the characteristics of elastic skid landing gear and the connection type of fuselage damper. This model not only considers the non-linearity of blade damper and fuselage damper， but also considers the influence of the non-proportional damping of fuselage damper on fuselage inherent characteristics. The stable fuselage modal responses are excited by the excitation method， and the modal damping identification method is used to identify the modal damping of the transient response. The results show that the change in time domain is complex because of the non-linear and non-proportional fuselage damping. When the system is stable， the larger the amplitude of the steady-state response speed of the excited damper is， the more lagged its variation will be.