Abstract: By analyzing the upstream situation of saltwater intrusion in the Pearl River Delta, the study calculates the reservoir storage capacity demand of the local reservoir group in Zhuhai city as the first line of defense for water supply security based on the joint water resources allocation and management of the river basin and region. By comparing different water source combination scenarios, the study proposes the water supply security schemes and overall layout for Macao and Zhuhai cities. The scheme includes the construction of second phase of the Zhuyin Reservoir, Bainikeng Reservoir, and the expansion of Qianwu Reservoir, as well as the further enhancement of pumping stations and water supply pipelines to effectively solve the water supply security problems of Macao and Zhuhai cities. This study not only provides a practical and feasible solutions for water supply security in Macao and Zhuhai cities, but also provides useful reference for water resources management in other similar coastal areas.