The debris flows are a catastrophic natural phenomenon. The debris flows occur in mountainous areas and can have serious consequences, such as the destruction of roads and buildings, and even human casualties. One of the possible ways to study the debris flows is mathematical modeling, which allows to consider the complex areas where it is difficult to carry out the full-scale physical experiments. The rock fragments can come in different sizes and shapes. Thus, for modeling rockfalls and debris flows, it is advisable to take into account the polydispersity of the solid phase. We present the results of three-dimensional debris flow modeling using a multi-fluid model based on the continuum approach. The debris flow was consisted of rock granules (the average diameter was equal to 7.5 cm) with the liquid content. The flow motion is represented as the motion of four interacting continua (gas, liquid and two solid phases). We compared the obtained results of calculations with the experimental data and with the results of calculations using the two-fluid model. The values of the maximum height of the flow layer and the average flow velocity calculated using the multi-fluid model slightly exceed the experimental data and the calculated data using the two-fluid model. In the case of maximum height, the relative difference (in quantitative indicators) compared to the experiments did not exceed 18%. In the case of the average velocity the relative difference (in quantitative indicators) compared to the experiments is 4%. So we concluded, that the multi-fluid model can be used to simulate the debris flow.