A micro/macroscopic analysis of PD3 pearlitic steel with layered microstructure is carried on.Based on the compatibilit conditions of stress and strain at the interface between two layers as well as the mixed law of composites,constitutive equations of an effective homogeneous inclusion are obtained.combining these equations with the K B W self consistent model,the micro macroscopic transition has been estabilished.It turns out that the analysis is capable of determining the overall responses of materials as well as local stress evolution in microstructure under monotonic and cyclic loading.It is found that stress in the thin cementite layer is very high.This is caused by intersification of the local plastic flow of the soft ferrite layer in which more loading is transferred cycle by cycle to the hard phase.Furthermore,a strength dimension law that the strength is inversely proportional to the square root of the layer thickness is developed to explain the high strength of the cementite layer.