A model test was performed to study the failure progress of natural and reinforced slopes by a model box with the size of 1 m×2 m×4 m. The tests included three different grade angles of slope (30°

45° and 60°) and two patterns of slope surface (flat and convex). The failure of slope was induced by tilting the model box and the failure progress was recorded with digital camera. The crack propagation

form of landslide mass and gradient angle of the box were summarized and analyzed. The results show that the form of slope failure is three dimensional and depends on the grade angles and patterns of slope; given the same grade angle

the flat is more stable than the convex but almost same in crack location; the reinforced slope is more stable and has a different failure form. The study results are useful to understand better the progress and form of slope failure

and provide a scientific base for treatment of landslide.