Abstract: In the current period of territorial spatial planning, island cities, as relatively independent natural geographical units, have fragile and unique ecosystems. Therefore, it is necessary to formulate spatial planning based on the refined assessment of ecological security pattern. In this paper, Zhoushan Island is taken as the study area, and the remote sensing ecological index (RSEI) is adopted to evaluate the ecological environment quality. Island geographical characteristics and ecological processes are considered for construction of ecological security pattern. Based on the analysis of factors overlapping and spatial conflict, the spatial optimization scheme and partition control strategy of territorial spatial structure are proposed. The research results show that: (1) The ecological environment quality of Zhoushan island is generally good, but the spatial difference is significant. The high-value coverage ratio of RSEI is 60.94%, showing a three-circle increasing structure from shore to land. (2) The core ecological elements of "source-corridor-buffer zone" stabilize the ecological security of the whole island. Ecological sources accounted for 43.32%, occupying the core hinterland; There are 67 ecological corridors with a total length of 276.5 km, which are concentrated in the patch fragmentation area of the southern ecological source area. (3) Spatial conflicts are concentrated in the central and southern parts of the island, mainly caused by the expansion of new towns and industrial development, the spatial optimization scheme of "one axis-four corridors-five areas-nine capes" and the strategy of ecological restoration zoning of "core conservation area, buffer restoration area and optimization coordination area" are constructed. By contrast between land and sea, this study forms two optimal patterns of island cities, namely "internal source-external corridor-peripheral buffer" and "aggregate with outlines", aiming at provide reference for the ecological security pattern and territorial spatial planning of island cities.