Abstract: At present, there are few researches on gas insulated metal enclosed switchgear (GIS) abnormal vibration, particularly regarding the excitation sources and generation mechanisms. First, the force model is established, and the force source value of GIS vibration induced by box type is calculated. It is pointed out that the electric power between three-phase buses is the main excitation source of the main frequency vibration in normal operation. Poor contact will lead to the increase of contact repulsion force, and loose anchor bolts will lead to the change of natural frequency of the system, which affects the nonlinear vibration response characteristics. The shell of GIS equipment is studied according to thin-walled cylindrical shell, and the multi-order natural frequencies of typical GIS shell are calculated. An effective nonlinear vibration equation is established, and the mechanism of multi-frequency vibration signal generation in the nonlinear GIS system is obtained for the first time by analytical method. Finally, a vibration signal acquisition system is successfully developed. Typical mechanical defects are set on 550 kV GIS vibration. The experimental results show that the amplitude and frequency of vibration response excited by the system are consistent with the theoretical analysis results. The research results provide support and reference for the detection and diagnosis of GIS mechanical defects.