Abstract: High frequency traveling vibration of a fan casing may be excited by the wake of rotating fan blades.High vibration level of a fan casing was observed during the test of a turbofan engine,the causes were analyzed,and the vibration-absorbing measures were investigated.Then,a casing structural optimization method for reducing vibration was proposed.Vibration experiments for casings before and after optimization were carried out.The results indicate that the optimization method is very efficient.