Accurately obtaining multiple-field information on the reservoir landslide subjected to dynamic water action is an important basis for reliably evaluating landslide stability. To overcome the limitations of GeoStudio and FLAC3D numerical software in simulating multiple-field information of reservoir landslides, this paper proposes a method for simulating multiple-field information of reservoir landslides with mutual feedback between GeoStudio and FLAC3D. This method first simulates the time-varying seepage field of landslides under dynamic water action using GeoStudio and then achieves fast conversion of the GeoStudio model and seepage field to FLAC3D by developing an interface program. Based on the hydrological characteristics of the rock-soil mass and the principle of effective stress, the soil parameters and initial stress in the FLAC3D model are modified to calculate the stress and strain of the landslide. The effectiveness of this method is verified by a large-scale physical model test of a reservoir landslide under a sudden drop in reservoir water level. It can be observed that the simulated evolution trend of multiple-field information of landslides using this method is consistent with the physical model test results. The maximum average simulation error of pore water pressure at monitoring points is less than 10%, and the maximum average simulation error of total stress is within 33%. The simulation results accurately reproduce the traction multiple slip surface failure mode and final slip surface location of the reservoir landslide physical model test.