An immersed boundary (IB)-lattice Boltzmamm method (LBM) coupled model is utilized to study the particle focusing in a straight microchannel.The LBM is used to solve the incompressible fluid flow over a regular Eulerian grid,while the IB method is employed to couple the bead-spring model which represents the fluidparticle interaction.After model validation,the simulations for hydrodynamic focusing of the single and multi particles are performed.The particles can be focused into the equilibrium positions under the pressure gradient and self-rotation induced forces,and the particle radius and Reynolds number are the key parameters influencing the focusing dynamics.This work demonstrates the potential usefulness of the IB-LBM model in studying the particle hydrodynamic focusing.