Abstract: The numerical simulation of the two-dimensional,viscous and axisymmetric flowfield and various diameter particle trajectories in a inertial Inlet Particle Separator(IPS)has been completed.Forthe complex boundaries,a grid system of the non-orthogonal body-fitted coordinates is generated,which is ideally suitable to this case;For the split flow,multiply connected regions are transferred to simple connected region.A SIMPLEC agorithm for the full Navier-Stokes solver in generalized curvilinear coordinates is applied to calculate the viscous flow in the IPS.At last,the particle trajectories in the above viscous flowfield and separator efficiency are obtained.Good agreement between the experimental data and predicted results indicates that the presented procedure and its program contribute to development and design of future high perfomance inlet particle separator.