<p>Sandstone serves as a vital medium for CO₂ geological storage. Wettability is a key parameter in assessing the CO₂ storage capacity and the safety of sequestration within sandstone reservoirs. This article offers a comprehensive review of the mechanism underlying the wettability alteration (WA) in sandstone reservoirs subsequent to CO₂ injection. It commences by reviewing the classification of wettability in sandstone reservoirs, elucidating the pros and cons of diverse methods and techniques used to measure sandstone wettability. Special attention is then given to the analysis of crucial parameters, including the phase state of CO₂, storage conditions, initial wetting state, and chemical reactions. Their impacts on the WA of the CO₂/brine/sandstone system are thoroughly evaluated. The paper also presents an overview of the latest research advancements in contact angle characterization through different methods over the years. It identifies the knowledge gaps existing in the inconsistent results of various characterization methods and in understanding the WA mechanism. Consequently, it proposes the imperative need for multi-scale quantitative wettability characterization and enhanced research on the wettability alteration mechanism. Finally, it underscores the significant influence of WA on the CO₂ residual storage capacity. This review provides a valuable reference for the selection of optimal formations for future CO₂ sequestration, as well as for the further assessment and implementation of CO₂ geological storage projects.</p>