Graphene oxide (GO) is a nanomaterial with ultra-high strength, good hydrophilicity, and dispersibility. To study the effect of GO on chloride penetration resistance of recycled concrete, the mechanism of action is investigated. The electric flux method is used to test the chloride penetration in recycled concrete specimens with 0, 0.03%, 0.06%, and 0.09% of GO. The volume change, microscopic pore distribution, and micro-structure morphology are characterized using laser rangefinder, and techniques such as X-ray tomography and scanning electron microscopy. The results show that the "coagulation nodule" effect of GO provides a growth basis for cement hydration,which results in a more uniform distribution of the hydrate microcrystals. It fills the micro-cracks of the recycled concrete, reduces the most probable aperture, increases the number of harmless small apertures, and enhances the volume stability of recycled concrete, thereby improving the chloride penetration resistance, which is important for improving the durability of concrete.