Abundant solid materials were formed as a result of landslide and collapse due to Wenchuan earthquake.The solid source around mountains would form a debris flow when appropriate rain condition occurs.Such a debris flow is structurally very large and strong,and the river flow can hardly wash away the deposit when the debris flow enters into the mainstream.As a result,the deposit on the river bed due to debris flow will cause a series of hazards.Based on the previous researches and relevant data,this paper simplified the interaction between debris flow and current of the main river,and adopted the finite element characteristic-based-split algorithm which is favorable to the stabilization of dealing with the convection.Finally,the numerical model of the confluence of debris flow deposit and main river was developed,and the deposit progress of the mega-debris flow from Wenjiagou in Mianyuan river was reproduced.Furthermore,the influence of the deposit on the flow route of the main river,and distribution of velocity and water depth were analyzed.The results showed that the simulation deposit terrain qualitatively agreed with the field data through comparison,including the deposit area and depth distribution.Furthermore,the improvement of the model in future was discussed. Abundant solid materials were formed as a result of landslide and collapse due to Wenchuan earthquake.The solid source around mountains would would a debris flow when appropriate rain condition occurs.Such a debris flow is structurally very large and strong, and the river flow can hardly wash away the deposit when the debris flow enters into the mainstream .As a result, the deposit on the river bed due to debris flow will cause a series of hazards.Based on the previous researches and relevant data, this paper simplified the interaction between debris flow and current of the main river, and adopted the finite element characteristic-based-split algorithm which is favorable to the stabilization of dealing with the convection. Finally, the numerical model of the confluence of debris flow deposit and main river was developed, and the deposit progress of the mega-debris flow from Wenjiagou in Mianyuan river was reproduced .Furthermore, the influence of the deposit on the flow route of the main river, an d distribution of velocity and water depth were analyzed. The results showed that the simulation deposit terrain qualitatively agreed with the field data through comparison, including the deposit area and depth distribution. Future, the improvement of the model in future was discussed.