The invention discloses a physical model test device and a test method for testing the stability of a landslide. The test device comprises a test slot, and further comprises a pore water pressure loading system, a pore water pressure measurement system embedded into a sliding belt, and a pore water pressure distribution system for realizing the change of pore water pressure of the landslide, wherein a sliding bed, the sliding belt and a sliding body are stacked in the test slot, and a laser range finder is arranged inside the test slot for measuring and recording the displacement variation ofthe sliding body during the landslide damage process; and the pore water pressure loading system is connected to the pore water pressure distribution system. The method for testing the stability of the landslide includes the following steps of: stacking a physical model of the landslide in the test slot, adjusting the water pressure value of the pore water pressure loading system to a preset valuep0, and loading the water pressure into the sliding belt until the pore water pressure in the sliding belt is consistent with a preset value and maintained; increasing the water pressure loading value step by step until the physical model of the landslide is destroyed; and quantitatively evaluating the stability of the landslide by calculating the safety abundance value of the landslide.