Abstract: Based on the detailed study of the regional geological setting as well as the supracrustal structure in the Yanshan area, we have shown what should be followed in calculating the balanced section of the Mesozoic deformation and determined the main decollement surfaces.Three main balanced sections have been constructed.The results are checked by various data of strain measurements.As a result, we have a shortening of 27.9% of the Yanshan orogen during the Indosinian and 10.9% during the Yanshan Movement of the giving a more accurate description of the Mesozoic deformational features of the area.