Steel slag as a large stock of bulk of industrial solid waste in China, the current domestic of its utilization is only 30%. The main reason limiting the large-scale resource utilization of steel slag is that the unstable substance in steel slag is easy to hydrate in water, resulting in the volume expansion of steel slag. By using linear variable displacement transducer (LVDT) test method, the expansion rate of asphalt trabecular specimen with steel slag was measured, and the influences of steel slag mixing ratio, oil stone ratio and particle size of steel slag on the expansion rate of the mixture were explored. The results show that the expansion rate of the mixture can be controlled more effectively when steel slag is not more than 50% of the mixture, the actual oil stone ratio of the mixture is increased by 1.5% on the basis of the optimal oil stone ratio, and using large steel slag. In addition, the active substance in the steel slag is constantly hydrated, which will lead to local expansion and aggregate spalling and other damage.