The utility model discloses a mid -board is used in tunnel construction belongs to civil engineering technical field, topping bar upright including left side pilot tunnel, median septum supports temporarily, left side pilot tunnel tops bar upright, and to support the lower extreme be temporary support to median septum temporarily, both are upright median septum, upright the mid -board supports thepreliminary bracing of topping bar of left side pilot tunnel through well pilot tunnel, preliminary bracing and the left side pilot tunnel preliminary bracing of getting out of a predicament or an embarrassing situation of topping bar of right side pilot tunnel, the preliminary bracing of getting out of a predicament or an embarrassing situation of right side pilot tunnel, well pilot tunnel supports the preliminary bracing of topping bar of left side pilot tunnel, the preliminary bracing of topping bar of right side pilot tunnel, left side pilot tunnel gets out of a predicament or an embarrassing situation preliminary bracing and right side pilot tunnel and gets out of a predicament or an embarrassing situation the preliminary bracing and constituteed one and strut with the same hoop of tunnel cross -section boundary phase, temporary support competent strutting still in addition, with the median septum mutually perpendicular that stands vertically, the hoop that temporary support's level was strutted around connecting through well pilot tunnel is strutted, upright the mid -board atress is reasonable, and the whole buckling failure of difficult emergence can not take place the continuous damage.