Understanding the mechanical properties of solidified oil-contaminated soil and the evolution of contaminant migration and diffusion under environmental effects is a key prerequisite for promoting the reuse of contaminated soil projects. Lime and fly ash with a low-carbon concept were selected as solidification materials. Combined with a leaching test and COMSOL Multiphysics software, the control of the solidification effect on oil migration under leaching environment was evaluated macroscopically by the oil content after leaching, and the mechanical stability under leaching was evaluated by soil strength and deformation. The results indicate that the solidification of lime-fly ash has the potential to address the issue of contaminant migration and diffusion, particularly in cases where a significant number of contaminants are migrating under the leaching effect of contaminated soil, and to achieve effective control of the migration of oil contaminants in soil. The oil content at each interface of solidified contaminated soil under the action of leaching is always close to the initial oil content setting state, and the migration rate is only 1.35%-2.76%. The variation range of the mechanical parameters of the solidified contaminated soil under leaching is positively correlated with confining pressure and contaminant concentration, but only fluctuates within 10 s of the initial stress and then the strength value is stable at 5.77×10⁴-6.07×10⁴ N/m², and the maximum fluctuation value of displacement is 1.73×10^-3-6.46×10^-2 mm. The mechanical stability of solidified contaminated soil is good, and the safety factor F_s is more than 10. Lime-fly ash solidified oil-contaminated soil can take into account both environmental and engineering requirements, and exhibits the potential for engineering reuse.