Abstract: A new arithematic model for describing the penetration process of both static cone penetro-meter and displaced pile tip in sand is presented.Theoretical solutions of cone rosistance,its effect range and critical depth,as well as side friction resistance are given from the medel.Theoretical rela-tionship between the cone penetration test data and the bearing capacity of pile are derived. It can indi-cate the scale-effect and depth-effect and is in good agreement with empirical formulas and test data.