Abstract: With the rapid urbanization and frequent artificial construction activities, the water network area in southern Jiangsu Province is facing a series of ecological and environmental problems, and ecological risks are becoming increasingly prominent. Constructing an ecological security pattern based on landscape ecological risk assessment is a powerful way to enhance the stability of the regional ecological environment. In this study, we took the Baixian Lake area of Suzhou as an example, and we adopted the landscape pattern index to construct a landscape ecological risk assessment model. The spatiotemporal differentiation characteristics of landscape ecological risks were analyzed in the study area from 2010 to 2020. We simulated the land use pattern under urban expansion scenarios based on the CA-Markov model, and predicted the spatial distribution of landscape ecological risks. On this basis, we explored the construction of ecological security pattern under the spatiotemporal dynamic evolution. The results indicated that: (1) The land use pattern changed significantly from 2010 to 2020. The area of construction land increased by 59.32 km2, while the area of farmland and water area decreased by 17.98km² and 53.61km² ,respectively. The area of forest land and grassland slightly increased by 12.27 km². The urban expansion scenario simulation indicated that the construction land would extend the most by 2030, with an increase of 134.14 km². The area of farmland and water area would decrease by 174.06km² and 6.76km² respectively. The total area of forest land and grassland would increase by 46.68km2. (2) From 2010 to 2020, the landscape ecological risk continued to increase. The proportion of medium risk and high risk areas increased by 6.55% in total, while the low and medium-low risk areas decreased by 4.62% and 1.92% respectively. The simulation of urban expansion in 2030 indicated that the proportion of medium-high ecological risk areas would increase by 10.12%, while the medium-low and low risk areas would decrease by 19.14%. (3) Based on the land use pattern in 2020 and the ecological security pattern under the urban expansion scenario simulation in 2030, we identified 23 ecological source areas, 50 ecological corridors, and 21 ecological nodes in the study area. A comprehensive ecological security pattern under spatiotemporal dynamic changes was constructed. The results may provide theoretical basis for protecting the ecological environment in water network areas and for resisting external ecological risks, which is significant for promoting regional ecological security development.