The deformation characteristics of large crosssection Tongzilin Tunnel on MiyiPanzhihua Section on ChengduKunming Railway located in Xigeda Fm strata and constructed by three bench+temporary invert arch method are studied by numerical simulation and site monitoring, so as to guarantee the stability of surrounding rocks during construction. The study results show that: 1) The deformations of surrounding rocks of large crosssection tunnel in Xigeda Fm strata are mainly along vertical direction. 2) The primary crown top settlement and crown top settlement induced by top heading excavation takes 41.3% in total settlement; and the advanced influencing range is 1.3D. 3) The crown top settlement and arch feet convergence are mainly affected by middle bench excavation. 4) The prediction formula for crown top settlement vs. time is U=102.105·exp(-5.33/X). 5) The prediction formula for horizontal convergence of arch feet vs. time is L1=19.552·exp(-7.49/X). 6) The prediction formula for horizontal convergence of tunnel wall waist vs. time is L2=17.862·exp(-23.26/X).