A great number of experiments show that pearlitic steel with Layer Meso-structure depend greatly on its struc- ture. Its fatigue life is marked influenced by the interlamellar spacing. Based on the finite element analysis of single pearlitic colony with different interlamellar spacings, the reason of the interlamellar spacing is investigated, which plays an important role in the mechanics behavior of single pearlitic colony. It is necessary to establish the relationship between the microstructure and the mechanics behavior of the pearlitic material, and the importance of the interlamellar spacing is introduced into the constitutive equation of Single Pearlitic Colony.