Abstract: A new bedload transport rate formula which considered the saltation load motion and the contact load motion was proposed.This formula overcame the shortage of present formulas whose accuracy mostly couldn’t be both acceptable when calculating the bedload transport rate under high and low flow dynamics.The finite state Markov process was used to describe the stochastic sediment interchanges.The sediment transform probability was modified for better description of sediment interchanges.According to a comprehensive consideration of the exposure angle,turbulence and the characteristics of bed sediments,the amounts of bedload was determined by the force analysis and the probabilistic statistics.After that,the new formula based on the stochastic sediment interchanges and the different motion patterns was derived by combining the saltation velocity and the slide velocity of bedload.Computations from this formula agree with both the results from indoor experiments and the in-situ observations,which cover the high and low flow dynamics.These agreements indicate this new formula could be used to estimate the bedload transport rate under different flow dynamics.