Nano-silica was used to improve the anti-MgSO4 erosion performance of solidified soil with soda residue and ground granulated blast furnace slag. The unconfined compressive strength (UCS), nuclear magnetic resonance and X-ray diffraction tests were carried out on solidified soil soaked in MgSO4 solution. The influences of nano-silica content, curing time and soaking time on strength and microstructure of solidified soil were studied. The results show that the sample with 3%(mass fraction) nano-silica content shows the smallest pore volume and highest UCS, and the products such as calcium aluminate hydrate are generated under standard maintenance conditions. In MgSO4 erosion environment, the samples cured for 7 d have good erosion resistance. When the silica powder content is 3% (mass fraction), the solidified soil has the best anti-MgSO4 erosion performance, and the unconfined compressive strength increases with the increase of soaking time. For the samples cured for 28 and 60 d, the anti-MgSO4 erosion performance is weaker. The functional relationship between UCS of solidified soil and nano-silica content and soaking time is given, and the minimum UCS is predicted. Appropriate nano-silica promotes the hydration rate and degree for solidified soil and reduces the generation of ettringite and its adverse effects, which improves anti-MgSO4 erosion performance for solidified soil with soda residue.