Suspension of sediment particles has been found to be in close association with the bursting process in a turbulent wall-layer flow. This mechanism forms the physical basis of the present heuristic turbulent diffusion model for suspended sediment in open channel flows. It is formulated using the bursting intensity and the mean duration of turbulent bursts. The bursting intensity as the fractional vertical turbulence intensity contributed by bursting is determined from its percentage, estimated using existing measured data, among the total vertical turbulence intensity calculated using an analytical solution in the literature. A skewed parabolic profile is obtained for the turbulent diffusion coefficient of suspended sediment. The unique parameter involved in the model is calibrated using measured data spanning wide ranges of suspension indices and sediment concentrations. It is found to increase with particle suspension index, indicating physically that more energetic turbulent bursts with longer durations are needed for the suspension of coarser and heavier particles. The developed model is shown to perform satisfactorily through comparison with independent laboratory data. Further refined models can be expected, given the enhanced understanding of the turbulent bursting phenomenon.