Abstract: Debris avalanches are frequently occurred in the mountainous region along the Sichuan-Tibet Railway in the Tibetan Plateau. These disasters are characterized by high and steep slope, huge energy and intense impact at the slope toe. In order to study the propagation behaviours and dynamic mechanisms of the debris avalanche, a series of laboratory experiments that grains aggregation freefall and impact on the horizontal plane then settle on it was conducted. In laboratory experiments, we consider the influences of the collision on the propagation and deposition features of debris avalanches. Images and quantitative data of the propagation and deposit features of the grains aggregation under the conditions of different particle sizes, volumes and falling height are obtained. The results show that (1) the bottom of the grains aggregation first hits the ground, then the particles are squeezed to form a shear surface. The particles move along the shear surface, spread and eventually deposit; (2) During the collision phase, the significant momentum transfer between the particles cause the particles at the front edge of the grains mass to move faster and farther, resulting in dispersive deposit; (3) From the center of the mass to the frontal edge of the deposit, the thickness gradually decreases; the shape is nearly circular at the beginning of the movement, and the final form is nearly diamond. The mechanical process leads to the occurrence of stress ridges; (4) The smaller the particle size of the grains aggregation is and the larger the volume is, the larger the maximum deposit thickness, the farther the travel distance of the main body, and the larger the main body cover area, the faster the spreading speed; the smaller the falling height is, the larger the maximum deposit thickness, the slower the spreading speed, which leading to a decreasing trend of the main body cover area; (5) Volume have the greatest influences on the deposit features of debris avalanches, followed by particle size, and the falling height has the least influence.