In the utilization of geophysical methods to detect underground water in karst mountain areas of Southwest China and the determination of suitable well position, the correct analysis and judgment of the properties of anomaly source and the choice of proper methods constitute the key to the successful exploration of underground water. Based on an analysis of the cases of successful water exploration in quite a few karst mountain areas in Long'an County of Guangxi, the authors put forward the geophysical water exploration model based on the combination of audio frequency telluric electric field method and audio frequency magnetotelluric sounding method, and made a tentative analysis of its exploration effect. Some experience concerning the determination of suitable well position was summed up as reference for water exploration workers in this region.