It is of great importance to study the safety control technology for shield boring in loess. The shieldbored tunnels of Xi’an Metro, which are located in loess strata, have to cross underneath complex ground surface conditions, cultural relics, buildings and structures. The shieldbored tunnel from Anyuanmen station to Beidajie station on Line 2 of Xi’an Metro crosses underneath a moat arch bridge. In the paper, the deformation of the moat arch bridge caused by shield boring is analyzed by means of FLAC3D program. The calculation result shows that the ground below the moat arch bridge has to be consolidated before shield boring, so as to ensure the safety and stability of the bridge. It is proposed that sand bags should be piled in the moat arch bridge zone and Soletanche grouting should be conducted behind the foundation of the bridge. The site measurement shows that the deformation of the moat arch bridge is within the allowance scope and the countermeasures taken are rational and effective.