Three kinds of activated coal gangue powder(AGP A, AGP B, AGP C) and limestone ore powder(LS) were selected to prepare SBS modified asphalt mortar with different filler asphalt ratios. The pavement performance of SBS modified asphalt mortar was compared and the modification mechanism of activated gangue powder and SBS composite modified asphalt mortar was analyzed. The results show that compared with mineral powder, activated coal gangue powder has smaller particle size, larger specific surface area, rougher surface and has more porous, active ingredients and transition metal elements, thereby improving the surface wettability and interface adsorption of activated coal gangue powder with SBS modified asphalt. The bridging action of activated coal gangue powder strengthens the network structure of SBS modified asphalt mortar，results in improving the high temperature performance of SBS modified asphalt mortar. However, the low temperature performance of SBS modified asphalt mortar is reduced because activated coal gangue powder pore absorbs light components of SBS modified asphalt.