Abstract: With the continuous development of urban underground space, foundation pits are often affected by their complex environment, which makes the increase of support design difficulties and construction costs. Therefore, environmental impact control is a key issue that needs to be focused on in design and construction of deep foundation pit engineering in the future. Taking the support design of a four-level ultra-large and deep foundation pit in Chengdu as a case study, this paper innovatively adopts technical methods such as hierarchical space combination support, temporary reserved soil platform, optimized layout of locally open-type pile rows, and symmetrical excavation on both sides of the pipe gallery based on time-space effect through scheme comparison, which economically and reasonably solves the technical difficulties of support. A structural safety assessment is conducted on the entire process of excavation and backfilling of foundation pits using Midas GTS. The rationality of the design scheme is verified by the later monitoring data, which provides reference for the support design of deep and large foundation pits in similar complex environments.