According to the principle of relative motion,a quasi-steady numerical model was proposed to describe the stable motion of a rigid spherical particle in an infinite straight channel.Based on the model and by using CFD(computational fluid dynamics)technique,the spatial features and influence mechanism of lateral lift were numerically investigated when a rigid spherical particle with certain size moving in a square cross sectional micro channel,and the components of lift were also discussed.The results indicate that the lateral lift shows a regular spatial distribution along the y direction.Meanwhile the magnitude of the lift changes from positive to negative in the radial direction,with unique radial position of zero lift,which is just the equilibrium position for the inertial focus of particles.The lateral lift consists of two components,the pressure lift and shear lift,in which the pressure lift is the determinant factor to the inertial focus of particles.