Based on the research development of ecosystem characteristics, theory and technology modes in Guangdong-Hongkong-Macao Greater Bay Area, Tokyo bay Area and San Francisco Bay Area, this paper summarizes the emerging ecological problems in main bay areas at home and abroad and the mechanism and driving factors of ecosystem degradation. Using the methods of meta and comprehensive analysis, we clarify the concepts, connotations, theory, technology modes, and case studies of ecological restoration in bay areas. The results show that: (1) the ecosystem characteristics of three main bay areas reveal that forest ecosystem takes the highest percentage, followed by cropland or grassland ecosystem, and then urban ecosystem. Forest ecosystem is usually distributed in the surrounding of bay areas, while urban ecosystem is in the estuary delta area. (2) The theory of ecological restoration in bay areas mainly takes the principle of restoration ecology, landscape ecology and compound ecosystem ecology as the foundation. Four types of the ecological restoration are remediation, rehabilitation, restoration and reclamation. (3) Technology modes of ecological restoration in bay areas include three modes such as active restoration, passive restoration and creation. Finally, the recommendations and prospects of ecological restoration practice in China and Guangdong province are put forward, in order to provide theoretical guidance for the ecological restoration of Guangdong-Hongkong-Macao Greater Bay Area.