Abstract: Potential for geological carbon dioxide storage in saline aquifers in Chinese maritime territories is substantial. However, considerable disparities in storage efficiency complicated the determination of the effective storage capacity. To enhance the accuracy and regional applicability of effective storage capacity estimation, we reviewed the key factors influencing efficiency coefficients and identified globally applicable methods for the calculation. By integrating seismic, drilling, logging, and core data, we employed statistical techniques for parameter optimization, with which both precision and accuracy of the calculations were improved. Additionally, we proposed a workflow from selecting and calculating efficiency coefficients based on various data sources. The saline water in clastic rocks in the Xihu sag, East China Sea was studied as the case. Results show that saline water in the Yuquan Formation and Longjing Formation are characterized by rich sand bodies with large thickness and multiple sets of reservoir-caprock. Among them, delta plain channel bar deposits are favorable microfacies for CO₂ sequestration. Specifically, the storage efficiency of the Yuquan Formation is 6.9%, which is 2.9% higher than that of the Longjing Formation. Based on the storage efficiency, we estimated that the effective storage capacity of the saline aquifers in the Yuquan and Longjing formations in the Xihu Sag is approximately 820 million tons. The Yuquan Formation in the western slope zone exhibits the highest storage potential and could be the optimal place for CO₂ sequestration in the Xihu Sag, and can be also considered a good candidate of a pilot area for CO₂ sequestration.