•SCA reduces hydrophilicity to enhance BF water damage resistance and compatibility with asphalt.•SCA makes BF surface become rough to enhance chemical bonding and mechanical occlusion effect.•Better adhesion and force-transmitting between BF and asphalt helps to gain stronger interaction.•SCA heightens low and high temperature mechanical performances of fiber-reinforced asphalt. The main goal of our work was to study mechanism of interfacial adhesion between basalt fiber and asphalt. Solution of silane coupling agent (2.5 wt%, KH-550) was used to modify fiber surface. Modified fibers were then used for fiber-reinforced asphalt fabrication with different fiber concentrations (0.5, 1.0 and 1.5 wt%). Samples were analyzed by DMA, DSR, EDS, ESEM, ACAM and FTIR. Treatment with KH-550 resulted in fibers with rough surface and weak hydrophilicity. It also increased surface area of fibers, improved their compatibility with asphalt and enhanced their chemical bonding with asphalt, all of which resulted in overall increase of mechanical performance of asphalt. Our research provides foundation for fiber surface modification for applications in road pavement engineering.