Abstract: The mode analysis method for multi-degree-of-freedom system, model uncoupling and order reduction method, the digital simulating method for nonlinear system, system identification and parameter estimation techniques and various available calculating method are synthetically used in this paper, to present the engineering calculating method for the fundamental frequency, establish the nonlinear approach model of the mechanical system and analysis the system dynamic characteristic, finally, give the equivalent linear model of the mechanical system and discuss the relation between various major parameters and handling quality.In reference to the model uncoupling part, it has been proved by the report of flying test. The structure of equivalent linear model have been demonstrated by the experiment of a control system.The analysis method of this paper may generally be used to the dynamic analysis for multi-degree-of-freedom mechanical system.