Using the mixing length of sediment-laden flow constructed with data fitting and combining the Prandtl mixing length theory, a new equation describing the velocity distribution of sediment-laden flow was established. Based on this new equation and the analogy of the relationship between the momentum transfer coefficient and mixing length, a new equation describing the vertical distribution of sediment concentration was also established. Through verification with observed data from the flume experiment and field survey, it was found that these two equations can objectively describe the vertical variations of velocity and sediment concentration, showing a higher precision in describing the sediment concentration. The error analysis shows that the error of the near-bottom velocity is large, indicating that the selection and judgment of the bottom boundary layer need further investigation; the error of the sediment concentration close to the surface is large, indicating that the selection of the reference point for the sediment concentration requires further theoretical research, in order to discard the influence of random effects.