The wettability of porous media is an important parameter in the process of CO₂ geological storage. Based on the wettability measurements and optical imaging techniques, the wettability measurement techniques of porous media at different scales under CO₂ storage conditions were reviewed, and the related wettability phenomena were analyzed. At present, the rock wettability measurements are mainly described from the measurement of surface wettability at the laboratory scale, the contact angle at the porous inner surface, and the overall wettability evaluation of core samples at the macro scale. It was shown that the pore structure, mineral composition, and surface roughness were critical factors for the pore-scale contact angle, affecting the mixed wetting characteristics of porous media and causing the wetting hysteresis phenomenon. The relationship between pore-scale and continuum-scale rock wettability was established based on the contact angle distribution in different local displacement events (such as drainage and imbibition). A recent study found that the rock wettability changed significantly during the drainage and imbibition process with the development of the displacement process. However, the correlation between the wettability of rocks at different scales and the mechanism of wettability alternation still need to be further studied.