Diffusion is a common phenomenon in many engineering fields. Most diffusion models use the classic Fick's law, which only consider the driving force due to ion concentration gradient in ideal solution. However, the influence of multi-ions environment on ion diffusion fails to embody in Fick's law. The electrostatic interaction between ions in the solution causes the solution to deviate from the ideal state which leads to the concentration of ions failing to fully exert, so the actual diffusion phenomenon cannot be properly explained. By applying the linear diffusion flux equation, introducing the modified Guntelberg activity coefficient to show the deviation of ion concentration between the ideal and actual solution, And combing with the mass balance equation together, a non-steady state diffusion model for multi-ions in non-ideal system was proposed. The effectiveness of the proposed model is verified and validated by comparing with the experiment results. The finite element software Comsol Multiphysics was used to conduct a series of numerical simulations. The results showed that the non-ideal of the solution has significant retardation effect on ion diffusion. When the ion valence state is fixed, the higher the initial concentration of ions, the more obvious the retardation effect on diffusion. When the concentration of contaminated source keeps constant, the greater retardation the retardation effect on diffusion.