The flow around a square cylinder confined in a two-dimensional channel is investigated for Re = 100 using the lattice Boltzmann method(LBM).Three blockage ratios are considered.The effects of channel walls on drag and lift coefficients of cylinder,Strouhal number and vortex structures in the wake of the cylinder are examined.The variations of the coefficients and the Strouhal number with the blockage ratio are presented.It is found that both the drag coefficient and the Strouhal number increase with the blockage ratio while the lift coefficient decreases.The drag coefficient increases as much as 30% compared to that for an unconfined square cylinder.The results are compared with related experimental data in literature and a good agreement is achieved.The comparison also shows that the LBM has capability in simulating bluff body flows.