CO convective dissolution has been regarded as one of the fundamental mechanisms to accelerate the mass transfer of CO into brine. We present a new spectrophotometric method to characterize the convective instability and measure the dissolved CO mass, which enables the real-time quantitative visualization of CO/brine transport mechanisms. Successive images were captured to identify the finger development regimes, and the convection morphologies were analyzed by the fingers length and affected area. CO solubility was experimentally studied, and the results are in agreement with the theoretical calculations. CO mass transfer flux was investigated as the Sherwood number changed. The increase in salinity and temperature has a negative effect on CO dissolution; here, numerical simulation and experimental phenomena are qualitatively consistent. In general, these findings confirm the feasibility of the method and improve the understanding of the physical process of CO convective dissolution, which can help assess the CO solubility trapping mass.