Yanliangshan tunnel is a key engineering site in Chongqing to Huaihua Railway. The tunnel passes through the Maoba syncline formed by carbonate rocks with very complex geological setting.The author conducted the applied research of more than one geophysical exploration methods in the tunnel and reached some conclusions. In geological beforehand forecast in the relatively deeply buried and long tunnel of carbonate rocks, we should first carry out controllable audio-frequency terrestrial electromagnetic exploration to find out positions, shapes, sizes and burial depths of various structures, karst areas and oil-gas reservoirs so as to get semi-quantitative understanding of the geological background. On such a basis, the negative visual velocity seismic reflection method should be used near the mined face so as to exactly detect unfavorable geological conditions in front of the face.