In order to investigate the effect of steel slag fine power (SSFP) on performance of asphalt mortar and mixture, SSFP was prepared using steel slag with a particle size less than 5 mm. With limestone powder (LP) as a comparison group, the performance of SSFP asphalt mortar was analyzed and evaluated with different filler-asphalt ratio (F/A), and the effect of SSFP on the performance of asphalt mixture was also investigated. The results show that, compared with LP, SSFP improves the high temperature performance, low temperature performance and fatigue performance of asphalt mortar and mixture, with the greatest improvement in low temperature performance, 190.57% for bending creep stiffness modulus of SSFP asphalt mortar and 9.93% for low temperature bending fracture strain of mixture. The increase of F/A improves the high temperature performance of asphalt mortar, but damages its fatigue performance and low temperature performance. The application of SSFP in asphalt mixture has strong feasibility and popularization value.