Coal mine goafs, large karst caves, loose debris ground and rich water are encountered during the construction of Yufengshan tunnel on Outer Ring Road of Chongqing.  "Top heading and bench" method with preserved core soil, CRD method, single side drift method and double side drift method are used in the tunnel construction and safe construction is ensured. Taking the construction of Yufengshan tunnel as an example, the author presents the excavation method and assistant construction methods for tunneling through the filling area of large karst caves and loose debris ground and summarizes the construction technology for threelane highway tunnels with large crosssections located in soft ground, hoping to provide reference for similar projects in the future.