The invention relates to an experiment device for simulating mud-rock flow motion and an experiment method thereof. The experiment device comprises a material box, a water trough which is connected with one end of the material box, and an accumulating panel which is connected with one end of the water trough. One end, which is connected with the water trough, of the material box is provided with amanual handholding controlling type gate. The experiment device further comprises the components of an ultrasonic distance measuring sensor which is configured above the water trough and the accumulating panel in a matching manner, a force sensor module which is arranged at bottom of the water trough and the accumulating panel in a matching manner, a synchronous data acquisition system and a high-speed image camera, wherein the synchronous data acquisition system and the high-speed image camera are configured outside the water tank in a matching manner. The experiment device can realize simulation for movement of the mud-rock flow and can observe and research an accumulation characteristic of the mud-rock flow in an accumulating sector. The device and the method can be used for researching interaction between the mud-rock flow and a dam structure. The experiment device and the experiment method settle a problem of incapability of effectively acquiring a mud-rock flow substrate stressstate by an existing mud-rock flow simulating device and realize synchronous measurement for flow depth, aperture water pressure, direct stress and shear stress in a mud-rock flow movement process.