The effects of potassium, sodium, calcium and magnesium four cation types of chloride salt on chloride diffusion properties of fly ash concrete were studied by RCM method and natural diffusion method. Based on molecular dynamics simulation, the radial distribution functions and mean square displacement curves of K+, Na+, Ca2+, Mg2+ and Cl- five types of ions in aqueous solution were analyzed. The results show that the chloride diffusion coefficient of fly ash concrete is mainly affected by the valence state of cations. The higher the valence state is, the greater the diffusion coefficient is. The diffusion coefficient first increases and then decreases with the increase of chloride ion concentration, and the diffusion coefficient first decreases and then increases with the increase of fly ash content. The reason that cation types affect the chloride diffusion property is the different diffusion capacities of ions. The order of hydration capacity of each ion is Mg2+>Ca2+>Na+>K+>Cl-, and the order of self-diffusion coefficient is Mg2+>Ca2+>Cl->K+>Na+. Mg2+ and Cl- in MgCl2 both have corrosive effect on fly ash concrete, and Mg2+ inhibits the excitation of fly ash activity.