To solve the problem of deterioration of concrete performance caused by low temperature in cold regions. Based on the theory of nanomaterials to improve the properties of concrete, the effect of nano-silica on the properties of concrete was studied from the macro and micro scales. The results of the compressive strength test show that the compressive strength of ordinary concrete is attenuated by about 10% under low temperature curing. After being mixed with nano silica, the compressive strength of concrete is increased by about 20%, and the optimal dosage is 2%. The improvement mechanism of nano-silica on concrete properties was explored through microscopic test data such as mercury intrusion, X-ray diffraction and scanning electron microscopy. The results show that nano-silica can promote cement hydration at room temperature and low temperature curing, consume calcium hydroxide generated by hydration, and produce more hydrated calcium silicate and hydrated calcium aluminate gel, thereby reducing the porosity of concrete, optimizing the microstructure of concrete, and improving the performance of concrete. Compared with the room temperature environment, the improvement effect of nano-silica on concrete at low temperature is slightly reduced, but it completely overcomes the adverse effects of low temperatures on the performance of ordinary concrete.