Present study describes a method to predict fine sediment runoff in drainage basins where numerous landslides and debris flows take place owing to heavy rain falls. Specially, the Akadani drainage basin, which was damaged by landslides and debris flows in the rain fall event in July, 2017, is chosen for discussion. An entrainment of fine sediment into flow water is formulated based on mechanism of sediment erosion of a single debris cone. Statistical characteristics of many debris cones formed along main reaches are specified using results of field surveys and photo analyses as well as of the accumulated results obtained from debris flow studies. Combinig these, an integlated method to predict fine sediment runoff is proposed. The method predicts successfully fine sediment runoff that occurred in the Akadani basin, and it is useful for specification of the upper boundary condition in treating sediment issue.