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In this study, a hybrid desalination process based on carbon dioxide gas hydrate and capacitive deionization (CDI) is proposed to improve desalination performance. In this method, the formed gas hydrate crystals are dissociated and the produced water is conducted to the CDI process. To overcome the separation problem of the residual brine between hydrate crystals, a reactor that can be capable of compressing crystals was designed. Also, to improve the efficiency of the CDI process, electrodes were synthesized based on the activated carbon and their chemical properties modified using nitric acid. The performance of the gas hydrate, CDI, and hybrid desalination method examined for single and multi-salt aqueous solutions containing sodium, potassium, calcium, and magnesium with different concentrations. Also, the effects of the hydrate formation temperature, applied voltage, ion type and concentration on the ions removal efficiency have been investigated. The results showed that the compression of hydrate crystals in the hydrate desalination process, and using the modified activated carbon electrode in the CDI process could significantly improve the ions removal efficiency. The results showed that the proposed method could remove around 82% of Na+ and 100% of K+, Ca2+ and Mg2+ from saltwater with similar concentrations to seawater, respectively. • A new hybrid desalination method based on gas hydrate and CDI process has been proposed. • Compression of hydrate crystals has a significant effect on ion removal efficiency. • Ion removal efficiency in CDI process is in the following order K+ > Na+ > Ca2+ > Mg2+. • The proposed hybrid desalination method can remove 100% of K+, Ca2+, and Mg2+. [ABSTRACT FROM AUTHOR]