A reversible simplified method was given to investigate the dynamic model for aero-engine high-pressure rotor system. By using the finite element method

the accurate complex dynamics model was built

and also simplified to gain the single-span with dual-disc model and single-disc model based on the center of mass concentration method. The critical whirling speed was compared for the simplified and complex models to indicate the correctness of the simplified method. This modeling-simplify method based on the structural characteristics made low-dimensional nonlinear dynamics analysis and parameter optimization possible with the consideration of the nonlinear factors of supporting

etc. And then the reversibility of the model-simplifying method was investigated. The new complex model and the discs' parameters of equivalent radius

thickness and location were obtained from the single-span with dual-disc model by the principle of optimized centroid location and the total mass of the discs. The 1th to 3th critical whirling speeds of the new complex model and the original model were compared

indicating that the errors were all less than 3%. The reversible model-simplifying method laid the foundation for the multistage-disc's engineering structural parameters design from the simple model structural parameters optimized by the nonlinear dynamics theory.