The effects of salt content and freeze-thaw cycles on the compressibility characteristics of modified saline soil in seasonally frozen regions were experimentally investigated by modifying the soil with microbial-induced calcite precipitation (MICP) combined with activated carbon. The results show that after MICP modification, the cementation effect of the generated calcium carbonate on soil particles can resist the expansion damage caused by salt-frost heave, and the compressibility is reduced. The addition of activated carbon promotes urease activity, making the MICP reaction more intense and thorough. This process generates more calcium carbonate to reinforce the soil structure. Furthermore, with the increase of activated carbon content, the reinforcement effect becomes more significant, and the compressibility is further reduced. However, with the increase of salt content, urease activity is inhibited, leading to a decrease in the urea hydrolysis rate. Consequently, the MICP effect becomes insignificant, unable to provide sufficient carbonate ions, and the calcium carbonate coverage area decreases. Therefore, MICP technology significantly improves the compression characteristics of saline soil in seasonally frozen regions.