Abstract: This paper analyzed incompatibility of surface deflection criteria and subgrade compressive strain criteria. The related exprssions between surface deflection and subgrade compressive strain is formulated by regression method. The concepts of design deflecion and pendssive dehon are clarified. The design deflection index to control subgrade compressive strain is introduced based on the relationship between surface deflection and subgrade compressive strain and on the compressive strain equation of AI designn method.