Identification of the ecological security pattern (ESP) is of great significance for the coordinated balance of regional economic sustainable development and ecological protection. This article focuses on the planning of the Pearl River Delta National Forest City Agglomeration. Methods such as Morphological Spatial Pattern Analysis (MSPA), Circuit Theory, and spatial design network analysis (sDNA) were applied to construct the development pattern of ecological networks before and after the Forest City Agglomeration construction in the Pearl River Delta. The spatiotemporal evolution of ecological landscape forms, topological connectivity, and the indicated ecological pattern were identified. Combining the land use and network connectivity characteristics of the planned functional zones, the study explored the identification of optimal spaces for the ecological security pattern in the forest city agglomeration of the Pearl River Delta. The results showed that: (1) In the change of ecological landscape morphology in 2015 and 2020, the core area and the length of ecological corridor increased significantly by 14.97% and 0.40%, respectively. The aggregation and connectivity of ecological patches are the main characteristics of the current ecological pattern change. (2) The connectivity potential of ecological barriers in the western and eastern forests and nature reserves, as well as the ecological protection belt along the southern coast (referred to as "two barriers and one belt"), has significantly increased. The proportions of highly connected, moderately-highly connected, and moderately-low connected ecological network structures have increased by 2.65%, 6.98%, and 8.25%, respectively, forming a reasonably improved ecological network connectivity structure. (3) Integrated the optimization targets of ecological source importance, ecological corridor connectivity and break points, to build priority protection and restoration of the identification criteria, we identified priority protection of important ecological source area for 14656.06 km², priority repair of ecological corridor with 930.69 km and 246 break points, further for exploring the path for spatial optimization identification and security pattern improvement. Overall, the forest city agglomeration in the Pearl River Delta formed an improved ecological security pattern with the "two barriers and one belt" in 2020. Ecological sources and the increase of network connectivity revealed the center of urban agglomeration ecological pattern improvement and the identification results of the ecological optimization space in the coastal protective belt. It indicates the necessity of strengthening the construction of urban agglomeration and coastal ecological corridor, and provides scientific reference for the identification of ecological security pattern and spatial optimization of forest urban agglomeration from the perspective of engineering restoration.