The TBM construction organization mode of one tunnel for two TBMs, i.e. the assembly and excavation of two TBMs carried out in a same tunnel, is adopted in a section of the second phase of water diversion project in North Xinjiang. In order to realize simultaneous assembly of 2 TBMs and rapid excavation, the combination method of engineering analogy and numerical calculation is adopted, the defects of original design form of assembly tunnel are analyzed, an optimization scheme is proposed, and the structural stress at the intersection of the main branch, where the structure has been changed lot, is calculated to ensure structural stability. The simultaneous assembly of 2 TBMs in optimized TBM assembly tunnel has been realized, rapid excavation has been achieved, and the construction schedule has been shortened.