A spring model is used to simulate the skeleton structure of the red blood cell(RBC)membrane and to study the red blood cell(RBC)rheology in Poiseuille flow with an immersed boundary method.The lateral migration properties of many cells in Poiseuille flow have been investigated.The authors also combine the above methodology with a distributed Lagrange multiplier/fictitious domain method to simulate the interaction of cells and neutrally buoyant particles in a microchannel for studying the margination of particles.