Compare with horizontal support, the bracing systems of pile and oblique brace have obvious advantages in deep excavation. However, because diagonal brace is inconvenient for the construction of structure , the use of this system is limited. Based on the coordinating space role of this support system, planning the excavation and exchanging brace and construction structure as a whole, according to the minimum potential result of a piecewise space unit, this paper introduces the model which are both applied to the excavation stage and exchanging brace stage, and derives the calculation method in relationship to the length of sub region. optimal design of the whole process was proposed for this form. Finally, the feasibility and rationality of the proposed method was verified by the practical engineering. And reached some signifecative conclusions, these can provide reference for the design and construction of such supporting system.