Abstract: The Dafengding tunnel is an extra-long deep tunnel in the seismically active mountainous region characterized by exceptionally complex geologic and hydrogeologic conditions in Southwest China. The primary challenges in the tunnel investigation arise from complex geological conditions and unfavorable exploration environments. Moreover, developing effective seismic mitigation measures necessitates precisely determining the fragmentation and water-bearing characteristics of rock masses at the tunnel site. Hence, based on the initial classification of regional lithologies using geologic data, this study conducted integrated geophysical exploration at the tunnel site by combining the audio-frequency magnetotelluric method with high-resolution electrical resistivity tomography. The results indicate that the integrated geophysical exploration effectively revealed the overall variation in apparent resistivity at the tunnel site and the shallow apparent resistivity distribution, particularly the characteristics of the electric field near the tunnel portal. These findings enabled the inference of the fragmentation and water-bearing characteristics of rock masses at the tunnel site. Moreover, the borehole data effectively validated the effectiveness of the integrated geophysical exploration, demonstrating that the integrated geophysical exploration can provide a valuable reference for the investigation and construction of extra-long deep tunnels in seismically active regions.