In order to investigate the effect of nano-SiO₂ on resistance of concrete to sulfate attack, concrete specimens mixed with 0%, 0.5%, 1.0%, 2.0%, and 3.0% (mass fraction, same as below) nano-SiO₂ were immersed in 5% (mass fraction) sodium sulfate solution for sulfate attack experiment in this paper. The effects of concrete specimens mixed with nano-SiO₂ on mass change, relative dynamic elastic modulus, loss coefficient of compressive strength, and resistance to sulfate attack in the accelerated sulfate attack experiment by wet-dry cycling were investigated. The results show that as the content of nano-SiO₂ increases, mass loss rate, relative dynamic elastic modulus and loss coefficient compressive strength of the concrete show an increasing and then decreasing trend. Compared with the NS0 group specimens, when the nano-SiO₂ content is 2% the performance of concrete is the best. Through X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis mechanism, it is found that the addition of nano-SiO₂ has a good improvement effect on improving the internal microstructure of concrete. Nano-SiO₂ can accelerate the hydration reaction inside the cement, promote the formation of hydrated calcium silicate gel, and form an interlaced dense network structure inside, further improving the compactness and resistance of concrete to sulfate attack.