A mixed-layer model can be used to simulate the velocity profile of debris flow under steady and uniform flow conditions. This model is deduced from an idea that the particles are no only dispersed throughout the entire depth but also concentrated more in the lower part of the flow under comparatively high solid concentration, and below the particle dispersive layer a macro-viscous layer appeares which may contain inter-particle friction drag. Theoretical velocity profiles are checked with some researchers' experimental data. It is found that the agreement is assuring and looks better than other equations for the velocity distribution.