First this paper established the dynamic equation for a typical flexible cantilever impact system by the Euler-Bernoulli principle, and gave the corresponding model analytical method. Then, based on some assumptions and definitions, the reducedorder model was given, which can embody the main characteristics, and the eigen-value of the system can be expressed deeply. Finally, the presented method was applied to the reducedorder process of the flexible cantilever impact system, and the method was illustrated by a corresponding numerical example. The results showed that the dynamic characteristics of the system can be exactly simulated by few modes, which provides a foundation for studing the control problem of the flexible impact system.