The energy absorption ability of a car rail during crash depends on the mean crush force of the rail.Themean crush force research helps to know the rail impact performance and reduce the potential defect at conceptdesign stage.However,as for the mean crush force,there is a considerable discrepancy among tests,simulationsand fitting results in literatures.In order to solve this problem,this paper analyzes the relationships between themean crush force and such parameters as the beam shape,beam thickness and mechanical properties of material bycombining physical tests with simulations.Then,a series of single- cell thin- walled rectangle section beams areemployed to carry out tests and simulations,and a new formula of mean crush force is deduced for the beams on thebasis of minimization principle of range,maximum deviation and standard deviation.The calculation results showthat the deduced formula achieves a fitting value which is closer to the simulation value than that in literatures,andit can meet the concept design requirement of frontal rail.