How to manage and control the existing construction land and cultivated land in the important ecological space, especially in the ecological conservation redline, is the focus of the current decision-making debate. Whether to withdraw, how to withdraw, and what impact it has are scientific issues worthy of academic discussion. This paper identified the important ecological space of Kunshan based on the framework of ecosystem service importance-ecological sensitivity-landscape connectivity, and analyzed the conflict characteristics and influencing factors between the important ecological space and its existing construction land and cultivated land. Moreover, the multi-scenario simulation was conducted to evaluate the response characteristics of regional ecosystem services under different withdrawal modes of the existing cultivated land and construction land in the important ecological space. The results showed that:(1) The importance of ecological space in Kunshan is distributed in a circle, gradually increasing from the center to the periphery. In the important ecological space accounting for less than a quarter of the entire region, the existing cultivated land and construction land are mainly distributed around the water area, and the conflicts with cultivated land are the main ones, accounting for 75.07% of all the conflict areas. The intensity of conflicts between the important ecological space and other land is significantly negatively correlated with the distance from major rivers. (2) Different withdrawal modes of existing cultivated land and construction land in the important ecological space will lead to different response characteristics of ecosystem services. Overall, ecological protection scenarios can effectively alleviate the trade-off relationship between different ecosystem services, but excessively ecological protection is not the most appropriate. Under the requirements of regional high-quality development, nation land spatial planning must pay attention to ecological protection, and the relationship of the existing different policies should be well balanced and the problem of "one size fits all" should be avoided in ecological protection. In addition, we attempted to explore the methods and ideas for the ecosystem services response characteristics to the different withdrawal modes of existing land patches in the important ecological space. Further studies on the area threshold, spatial configuration characteristics, and the ecosystem services response law of exit land patches can be carried out in the future. In-depth study of the response of the exit characteristics of existing construction land and cultivated land in the important ecological space has important theoretical and practical value for guiding land spatial planning and management.