WenXiang tunnel ,one of the tunnels constructed for the ZhengXi Special passenger Railway in china. In this project we have carried out a series of research on optimizing the construction method for shallow and large-span tunnels in loess condition. According to the field monitoring of ground settlement, vault settlement and primary support stress of the tunnel section before tunnelling underneath the LianHuo Highway, the result indicates that soil settlement and primary support stress can not be controlled very well, and current construction program needs to be reformed since it can not meet construction safety requirement. Our synthetical analysis comprises the optimized methods have been used in construction, such as reducing excavation area, increasing excavation steps of pilot tunnel, reserving core soil, closing invert punctually, reinforcing primary support, etc. The security and reliability also has been verified by numerial analysis sofeware FLAC3D. From feedback of field implement and monitoring result, the effect of optimized method is significant; and all of these methods ensured this tough project implemented successfully. These results derived from our research are subject to a ceritain value that could be referred for future analogous project , in terms of controlling soil settlement and protecting surrouding building facilities.