The chloride diffusion coefficients of C30 high performance concrete subjected to different unilateral load and freeze thaw cycle number at different curing age were measured by electro migration(RCM) tests. The function relations of chloride diffusion coefficients with different factors were established. The test results indicate that unilateral load, freeze thaw cycle number and curing age have significantly influence on chloride permeability in concrete. The relationship between chloride diffusion coefficients and load grade, freeze thaw cycle number and curing age is nearly suitable to quadratic polynomial, linear and power function relation respectively.