Abstract: First, fundamental relations on the surface energy density and surface elastic constitutive equations are derived based on the trans-scale mechanics theory considering both strain gradient and surface effects through energy variation. Second, a new method to determine both surface energy density and surface elastic parameters is developed based on a simple quasi-continuity scheme, Cauchy-Born rule. Furthermore, taking the face-centre-cubic (FCC) metals as examples, we systematically obtain the values of the surface elastic parameters for typical fcc metals which are consistent with others results by using the molecular dynamic simulations.