A mathematical model describing mean sediment concentration and turbulent boundary layer of wave-induced sheet flow is presented. The interaction of the fluid and sediment in two-phase flow is considered. The diffusion coefficient and eddy viscosity are respectively expressed as functions of gradient Richardson number, which measures the effect of suspended sediment on turbulent transfer of mass and momentum. Computational results reveal that the presence of suspended sediments retards mean velocity profile and its corresponding phase shift. The friction factor which differs from rough wall law is obtained from the integration of momentum equation. An explicit expression based on the approximation of friction factor is given to define the region where sheet flow occurs. Observations in the laboratory provide support for the validity of this criterion. The predicted mean concentration profile is compared favorably with measurements.