The tensile fatigue was enforced on C30 concrete with different maximum stress levels and different fatigue cycles. Residual tensile strain, fatigue damage degree based on ultrasonic velocity and damage resistance based on electrochemical impedance spectroscopy were used as the characterizations of fatigue damage to study the effect of tensile fatigue on the diffusion coefficient of chloride ion in concrete. It is shown that the diffusion coefficient of chloride ion in concrete increases with the increase of residual tensile strain. The residual tensile strain 25×10-6 could be used as a point where concrete starts degradation caused by chloride ion. The diffusion coefficient of chloride ion in concrete increases exponentially with the increase of fatigue damage degree. The diffusion coefficient of chloride ion in concrete decreases exponentially with the increase of damage resistance.