In the electro-chemical reinforcement method, the type of injecting solutions has been one of the main research issues. In order to study the effect of cation radius in injecting chemical solutions on the effect of electro-chemical reinforcement of soft soil foundation, Ca²⁺, Mg^2+, Cu²⁺ with different radii of the same valence were taken as the research objects, the changes of current, drainage volume, effective potential, electric permeability coefficient during the test and the distribution of water content and shear strength after test were analyzed, combined with scanning electron microscope(SEM) to explore the effect of different cations on the electro-chemical reinforcement effect. The results show that the electro-chemical method can effectively shorten the treatment time and improve the reinforcement effect compared with electro-osmosis method. Increasing the ionic radius of injected cations in the electrochemical method can significantly improve the conductivity, electric permeability coefficient and shear strength of the soil after treatment. Among them, the reinforcement effect of calcium ions is the best. The SEM images also show that soil compactness is higher after calcium ion treatment.