Abstract: With the growing scarcity of land resources, especially in coastal areas, much attention is paid to the efficient use of underground space.But with the excavations being dug deeper and deeper, the geotechnical conditions of the stratum become more and more complex.This situation leads to a series of problems in the aspect of safety and economy, which need to be solved quickly.So, referring to the project of Singapore Maritime Museum, it is introduced in detail the design and calculation- analysis of the envelope structure ofthree walls unified into one, it is expected to provide guidance for design and construction of excavations．