Abstract: Funing tunnel is one of the key Yungui railway tunnel,with complex geological conditions.In the engineering geological mapping,and on the basis of investigation mainly adopts the controlled source audio frequency magnetotelluric(CSAMT) method and deep drilling to detect the tunnel,it was checked out the tunnel rocks,geological structure,hydrogeological condition,surrounding rock level and anomaly zones,etc.Through the comparison of the geophysical exploration and drilling,it was found that CSAMT method lithology of interpretation accuracy was higher,hierarchies of surrounding rock was good,the interpretation of the fault accuracy rate was lower,strong in karst development or lithological changes caused by a broken rock,extremely weak or rich water zones for property characteristics similar,geophysical exploration is difficult to distinguish,and need to comprehensive analyzes.The CSAMT method is suitable for complex as long tunnel,but need to be with geological surveying and mapping,drilling for comprehensive interpretation.