Concrete is susceptible to external erosion during service, the life of which was thus shortened due to the deterioration from the surface to the inside. In this study, the concrete surface treatment agent at multi-scale was innovatively proposed, which compounded of nano-silica sol–gel, micron-scale lithium silicate and sodium silicate. The physical properties and mechanical properties were investigated. Moreover, the mechanism of the new surface treatment agent was revealed in terms of pore structure and hydration products by XRD, TG, NMR, iMicro, and SEM. The results show that the Mohs hardness, flexural strength, and hydration degree are increased (by 260%, 78.7%, 12.1%), and porosity is reduced by 22% after the surface treatment. The mechanism is that pores can be repaired by particles of multi-scale. In addition, pretreatment of Ca²⁺ can further promote the pozzolanic reaction. The extra of EDTA-2Na can promote not only the pozzolanic reaction but also secondary hydration reaction.