The invention discloses a method for improving properties of expansive soil by utilizing silica fume. The method realizes resource utilization of the silica fume by utilizing the silica fume to improve the expansive soil; the silica fume can be used for replacing or partially replacing the use of traditional expansive soil modifying agents such as lime and cement, so emission of greenhouse gases in cement and lime production processes is reduced, and the method satisfies the concept of sustainable development. The method disclosed by the invention gives an optimal mass mixing ratio of the silica fume as the expansive soil modifying agent; after the expansive soil is processed by using the silica fume of which the mixing amount is 3%, the swell-shrink characteristic of the expansive soil isobviously reduced, the improved expansive soil can maintain relatively good water stability in drying and watering circulation process and is free of surface peeling; and the improved expansive soilmeets the requirements of engineering fillers.