The construction of ultra largespan fourtrack tunnel, of which the excavation area equals to 6 times of that of traditional singletrack railway tunnel, is difficult; and there is no successful precedent. The construction methods for ultra largespan fourtrack deep tunnel on Wumengshan No. 2 exit section on LiupanshuiZhanyi Railway are studied by numerical simulation and site monitoring methods. The results show that: 1) By using temporary support replaced by prestressed anchor, the temporary support of arch is successfully dismantled, the replacing construction risk of arch is reduced; the disadvantages of traditional soft rock tunnel construction are overcome; the safety and flexibility of support dismantling are improved; and large working face can be provided for followed construction step. 2) By using temporary crossbrace replaced by prestressed anchor cable, the temporary crossbrace dismantling risk is avoided; and the construction flexibility is improved. 3) The threebench excavation of ultra largespan tunnel is realized by using temporary support replaced by prestressed anchor and temporary crossbrace replaced by prestressed anchor cable.