Supersulfated cement (SSC) is a kind of sustainable low-carbon, less clinker or no clinker cement, which suitable for use as a low grade concrete pavement repair material and has been widely concerned, but it needs to add a certain amount of alkali to activate its higher early strength. Therein, the bonding properties of SSC mortar modified by sodium silicate and high alkali red mud and its influence factors were studied, and influence mechanism was analyzed by simulating the bonding interface. In order to provide a theoretical basis for the application of SSC as low grade pavement repair material. Results show that the bonding strength between modified SSC repair mortar and the old substrate increased when the roughness of old substrate surface increased. When the load was applied, the stress of the bonding interface was significantly greater than the other specimen position and increase of the roughness was advantageous to the interface stress dispersion. Under the same roughness condition, the surface of the old matrix should not be too dry or wet, because the water migration will occur at the bonding interface, which making the W/C near the interface different from other regions, leading to the increase of micro-cracks at the interface and the decrease of bonding strength.