In order to investigate the chloride ion permeability resistance of lithium slag concrete under pressure circumstance, C20, C30 and C40 concrete with different content of lithium slag (0%, 10%, 20% and 30%, mass fraction) were designed in this paper. It applied 10%, 30% and 50% of the ultimate compressive load as continuous compressive stress to carry out the concrete chloride ion permeability tests. The results show that the electric flux increases with the increase of water-cement ratio when the water-cement ratio is in the range of 0.40 to 0.62. For the concrete with different stresses applied, the electric flux of C20 and C30 concrete increases significantly when the compressive stress ratio reaches 0.3, and the electric flux of C40 concrete increases significantly when the compressive stress ratio reaches 0.5. For the concrete with different lithium slag content, the electric flux decreases with the increase of lithium slag content. Taking Fick’s second law and the law of conservation of mass into consideration, the model of chloride ion permeability of lithium slag concrete was established under continuous load. The results show that the permeability of chloride ion in immersion environment is in accordance with the experimental law, and the simulation results are consistent with the experimental results as well.