A two-dimensional axisymmetric analysis model was established by using the finite element method. The migration and diffusion of heavy metal ions (Cu²⁺, Cd²⁺) in soil were studied. The migration characteristics of single heavy metal ions (Cu²⁺) and composite heavy metals (Cu-Cd) were compared. The diffusion of heavy metals before and after solidification were analyzed, and the influences of temperature and dry-wet interaction were considered. The results show that the migration radius of composite heavy metals is larger than that of single heavy metal ions in the infiltration process. The solidified contaminated soil has a good control on the diffusion rate of heavy metal ions, and the effect of solidification on the diffusion of single heavy metal ions is more obvious. The environmental temperature has a positive correlation effect on the diffusion rate and range of heavy metal ions, and the diffusion range of heavy metal ions increases significantly under wet and dry cycles.