The strength of resistance to chloride ion erosion has a key impact on the service life of cement-based materials. In this paper, the effect of different graphene oxide (GO) content (0%, 0.02%, 0.04%, 0.06%, 0.08%, 0.10%, mass fraction) on chloride ion erosion resistance of cement mortar under dry-wet alternating chloride environment was studied. The relationship between free chloride ion concentration and chloride ion erosion resistance of cement mortar under different GO content was analyzed, and the chloride ion erosion resistance of cement mortar was analyzed from micro perspective by scanning electron microscope. The results show that GO can significantly improve the chloride ion erosion resistance of cement mortar and the optimal content range is 0.04%~0.06%. At the same drilling depth, the free chloride ion concentration in cement mortar decreases first and then increases with the increase of GO content. GO can effectively regulate the microscopic morphology of cement mortar, reduce the generation of internal pores, make the structure more dense, and improve the ability of cement mortar to resist chloride ion erosion.