Karst areas and karst water are widely present in Guizhou Province.The interaction between tunnel construction and karst water has long beena problem encountered in railway projects in Guizhou. Using the Moxiong and Yinshan tunnelsas examples, this paper attempts to address this issue. Via the interpretation of magnetotelluric data and the application of MIDAS GTS, groundwater problem and its disharmonious relationship with the tunnel are analyzed.After the construction of the Moxiong tunnel was commenced, the groundwater level droppedand did not recoveras expected in the springs at nearby residences, leading to the withering of the springs and severe water shortage in the communities. Yinshan tunnel on the other hand had experienced asevere rainstorm, as a result the karst water pressure elevated and eventually blasted one of the vertical side walls, which damaged the tunnel in a length up to 20 meters, interrupting train pass for more than 24 hours. The lessons from these examples suggest that when selecting the tunnel line in Guizhou, the boundaries of karst water systems should be clarified to avoid the areas with well-developed karst water. In the design stage, full consideration should also be taken to avoid any possible hazard from karst water. During the construction of tunnels, the karst channels encountered should be dredged rather than plugged.