Motion of sediment particles in turbulent flows is usually a problem including multi-scale particle-turbulence interactions and is still far from being clearly understood. In this paper, an improved numerical method is proposed to describe the particle diffusion in inhomogeneous turbulent flows, in which the fluid motion is solved by the Reynolds-Averaged Navier–Stokes (RANS) equations while the particles are tracked with a Lagrange approach. For dilute problems, not only the inter-particle interactions but also the influence of particles on the fluid turbulence are all omitted. To simulate the stochastic motion of the sediment particles, a modified continuous random walk (CRW) model is employed, in which a highly effective correction to the particle drift is suggested to account for the effect of particle inertia. Enhancement of the particle velocity fluctuation due to vortex shedding in the particle wake is also taken into consideration. The model is then successfully verified through applying to the particle diffusion in steady turbulent pipe flows and to the suspension of neutrally buoyant as well as natural sediments in steady open-channel flows. The computational results are demonstrated to be in good agreement with the experimental data.