Abstract: Storing carbon dioxide (CO₂) underground is one of the effective measures to reduce greenhouse gas in the air, and the offshore geological storage is an important choice for CO₂ storage. Guangdong province is one of the most developed areas in China, which emits a large amount of CO₂. The CO₂ geological storage potential is limited onshore but great in offshore basins to the province. Therefore, the CO₂ offshore geological storage is significant to a low-carbon economy of Guangdong. In this paper, the Huizhou 21-1 structure, located in the Huizhou sag about 179 km from the coast, was selected as a case for offshore CO₂ injection and sequestration simulation. A 3-D model was built up and TOUGH2 Producer was used to do simulation. The migration, distribution, dissolution and formation pressure variation after CO₂ injection were studied. 8 comparison cases were used to analyze the impacts of permeability, porosity, salinity and vertical versus horizontal permeability ratio. Results indicate that the 3D model can provide a good description of the migration process and the distribution status of the CO₂ in the reservoir. One local seal in the Lower Zhujiang Formation presents an ineffective cap, because of its small thickness and relatively high permeability. Changes in permeability, porosity and vertical versus horizontal permeability ratio have significant effects on injection and sequestration in Huizhou 21-1 structure, but the salinity change, which varies in a range of 33~39, does not affect the process significantly.