The application of geophysical prospecting technologies, including seismic reflection wave technology, high density resistivity technology and high frequency magnetotelluric technology, in the exploration of a rivercrossing tunnel is presented. The seismic reflection wave technology is the first choice for the exploration of underwater projects. When the seismic reflection wave technology is used in underwater projects where the water is shallow and the media under water is hard, the prospecting result is not so accurate. When the seismic reflection wave technology is ineffective, high density resistivity technology and high frequency magnetotelluric technology are tried and good results are achieved. The reliability of the prospecting results is improved by means of mutual comparison and verification on the prospecting results obtained by different technologies.