The tunnel length of O47 Sanchong Elementary School station of CL700A project, Luchou line to the tunnel turnout of CK570C project , Sinjhuang line, Taipei MRT,totals up to 887m. Due to the insufficiency of the road width of Sanho road, sec1、2, Sanchong City, Taipei County where the shield tunnel goes underneath, the tunnels start in parallel direction from the workshaft of the station, gradually changing into overlap form according to the alignment of the tunnels towards the turnout of CK570C project , Sinjhuang line when passing the intersection of Sanho rd. sec2 and Changan street. Therefore, the onsite hydro pressure anchor caisson method for crosspassage 1 in this tunnel is introduced, in respect of its depth（33m）and environments where the road width is 8.5m and the crosspassage is only 2m away from the existing building. Usually In Taiwan, similar shafts which mostly are shallow are usually constructed with the selfweight caisson methods, whose construction precision is beyond control. The introduction of hydro pressure anchor caisson method is not only the first time in the mass transit system, but also the pioneer in civil works in Taiwan.