Abstract: The bed deformation and sediment transport result from the exchanges among various form of sediment motion.It is significant to take into account interaction among suspended load, bed load and movable bed to explore the mechanism of bed changes and improve modelling methods. Considering the influences of near-bed turbulence on the critical condition of suspending processes of sediment particles, a theoretical criterion is presented according to the concept of probability of suspension. In addition,several previous formulae are thus analysed and reviewed.