There are more and more pit-in-pit excavations in cities, which include inner pit and outer pit. Owing to the inner pit excavation, pit-in-pit problem aroused and brought about accidents. For this reason, based on the co-construction, deep, and large pit-in-pit of Shanghai Museum of Natural History and Metro Line 13, the excavation influence between inner pit and outer pit was analyzed. The deformation of underground diaphragm wall under the condition of three different distances between outer pit and inner pit were compared through centrifuge model tests. Then, the effect of excavation width of outer pit on underground diaphragm walls was researched through numerical analysis. Results show that the deformation of outer underground diaphragm wall increased with the excavation width of outer pit, for the inner pit, the opposite was true. The critical influence distance between outer pit and inner pit was within 22 meter and 24 meter. According to the critical distance, the area adverse to excavation pit stability was identified.