When highways and railways cross the karst area, appropriate route selection can reduce engineering cost, engineering diseases and environmental impacts, so the problem of crossing and avoiding will be scientifically solved. The proposed Guang’an to Linshui highway is four-lane width and of first-class standard. In the preliminary design stage, based on the engineering feasibility study, the A-line and the K-line schemes are two candidates. The Huayingshan super-long tunnel crosses karst area, which is a key construction of this project. The data available from existing G42 Shanghai-Rongshan expressway as another Huayingshan tunnel provides a basis for this study. Considering the karst development, hydrogeological conditions and the key points of highway route selection in karst areas, a varietyof auxiliary technologies were used to analyze the principle of route selection. Finally it is concluded that the K-line scheme is the optimal scheme. Through this project example, it is suggested that in the process of highway route selection in complex karst areas, the principle of "multi-comparison and careful selection" should be followed, and environmental protection should be practiced.