Abstract: Double-row piles-double diagonal bracing foundation pit support is a new type of foundation pit support system, which is composed of double-row piles-single diagonal bracing by adding purlins, coupling beams and two diagonal bracings. In order to explore mechanical characteristics and deformation control effect of the system in deep soft soil foundation pit engineering, a field test of double-row piles-double diagonal bracing foundation pit supporting system is carried out for the first time combined with a foundation pit project in Shanghai, and the applicability of the system is evaluated through the internal mechanical characteristics of the supporting system (the axial force of the front and back rows of diagonal bracing, the axial force of the coupling beam, etc.) and the monitoring analysis of the supporting structure deformation. At the same time, the finite element software Z-soil is used to carry out the numerical simulation analysis of the support system. By comparing the field monitoring data, the overall deformation law of the new support system is verified, and on this basis, some optimization analysis is carried out. The results show that the supporting system can be used in soft soil foundation pit engineering, and the front and back rows of diagonal bracing form an effective combined supporting effect through coupling beams. Compared with the double-row pile-single diagonal bracing structure, the supporting system has an obvious effect in controlling the horizontal deformation of the retaining wall and reducing the bending moment of the retaining pile body. In full consideration of the construction feasibility, convenience and support safety, the form of 50 ° front diagonal bracing + 55 ° rear diagonal bracing can maximize the joint support effect of double diagonal bracing, effectively control the horizontal deformation of the enclosure and the bending moment of the pile body. The above research results provide new insights and relevant references for the development of support systems for deep foundation pits in soft soil areas.