To conduct parameter optimization for threebench construction method of tunnels in deep waterrich rocks, the Zhengpantai tunnel of the Chongli highspeed railway is taken for an example to carry out surrounding rock stability analysis and parameter optimization using three level orthogonal tests of fluidsolid coupling numerical simulation considering the height of the heading, the length of the upper bench, the length of the lower bench, and the advancement step length as the parameters. The results show that: (1) The height of heading has an obvious influence on the crown settlement, the wall displacement, the intrusive displacement of the face, and the scope of the plastic zone. (2) In the grade Ⅳ rocks, the excavation height of the upper bench is 27.8% of the excavation span, reaching 4 m, and the upper bench and the lower bench length is 55.6% of the excavation span, reaching 8 m, and the length of advancement step is 20.8% of the excavation span, reaching 3 m.