Abstract: The bed failure model is the important initiated model for debris flow in channel. However, there is no detail critical condition for bed failure model. In this paper, a series of laboratory experiments were carried out to study the initiation of debris flow by runoff in the channel. The experiments were conducted for the initiation models and critical condition with different particle size, saturated density, internal friction angle, and permeability coefficient. It was found that the slope threshold of debris flow initiation in bed failure model with no cohesion sediment increased with the increasing of sediment saturation density and internal friction. The minimum slope was about 17 degree in the experiments for the bed failure. When the bed slope is greater than the threshold slope, the thickness of the saturated layer of the bed failure decreases with the increase of the bed slope, the minimum sediment saturation thickness may be 0. The critical discharge of debris flow in fluvial transport model is much larger than that in bed failure model. The critical discharge of debris flow in bed failure model is the production of the permeability coefficient of sediment, the depth of saturated water and the width of channel.