A new approach describing the flow stress of ferrite-pearlite steel has been proposed,which divided the deformation process into three stages based on whether ferrite or pearlite yielded.Isowork increment assumption was applied to describe the transfer of load between the components.The physically based model to describe ferrite was approximated with Swift's equation in order to obtain the analytic solution.The tensile strength of ferrite-pearlite had a linear relation with pearlite volume fraction,square root reciprocal of ferrite grain size and reciprocal of pearlite interlamellar spacing.Moreover,a model to calculate the tensile strength of ferrite-pearlite steel was proposed.The predicted values of tensile strength were in good agreement with experimental results when the pearlite volume fraction was less than 20％.Considering the plastic relaxation mechanisms,the internal stress was modified with pearlite volume fraction,total strain,yield stress of ferrite and pearlite when the pearlite volume fraction was more than 20％.