Abstract: CO₂ geological storage is a guaranteed technology for achieving carbon neutrality. The offshore deposit basin is far away from the human activity area, and the implementation of a CO₂ geological storage is more advantageous than the land sedimentary basin. To find out the CO₂ storage potential in the Weixinan sag of the Beibu Gulf Basin, based on the 8 indicators such as caprock burial depth, the maximum thickness of single layer mudstone, mud-soil ratio, fault density and reservoir porosity, formation thickness, sand-soil ratio, permeability, etc., it has established a reservoir evaluation system for the secondary structure unit of the basin. Combined with the core physical property data of lays and 3D geological models, the reservoir and caprock of the Weixinan sag are optimized, and the effective storage potential is evaluated with the US-DOE method. The results show that within 800−3000 meters below the sea floor, in the Weixinan sag, there are two sets of reservoir-cap combinations suitable for CO₂ storage. Combination 1: in Neogene, the neritic mudstone of the first member of the Jiaowei Formation is the cap rock, and the neritic sandstone of the second member of the Jiaowei Formation and the Xiayang Formation is the reservoir, and the effective storage capacity is 0.749 billion tons. Combination 2: in the Paleogene, the deep lake mudstone in the second member of the Weizhou Formation is the cap rock, and the sandstone in the third member of the Weizhou Formation is the reservoir, and the effective storage capacity is 0.374 billion tons. In the Weixinan sag, two sets of reservoir-cap assemblages suitable for CO₂ storage in the saline aquifers are selected, with an effective storage capacity of 1.123 billion tons. According to the evaluation of the annual CO₂ emission of 70 million tons in the west of Guangdong Province, it can meet the CO₂ emission reduction needs of the region for more than 16 years. Offshore geological storage is a potential path for the green and sustainable development of coastal heavy chemical clustering areas and to achieve the goal of carbon neutrality.