The treatment of heavy metal-contaminated soil has been a difficult problem for many years. In order to repair heavy metal-contaminated sites with high efficiency, convenience, and low cost, solid wastes red mud and fly ash were used as main curing agents to repair Cu2+-contaminated kaolin. Electrochemical impedance spectroscopy, unconfined compressive strength, and leaching toxicity measurement were carried out. The experimental results show that when the ratio of red mud to fly ash was 7∶3, the solidification effect of Cu2+ in contaminated soil was the best, and all test indexes complied with the national standards. Moreover, Electrochemical impedance spectroscopy was proved to be a convenient, accurate, and non-destructive method for evaluating solidification effect. Through this solidification method, the remediation cost can be reduced, and the principle of solid waste reuse car be met. The method is suitable for the remediation of heavy metal-contaminated sites.