A particle model for calculating turbine wake flow during the optimization of wind farm micro-siting is presented. This model treats the wake flow as virtual particles generated by the turbine rotor. Based on the pre-calculated flow field of empty wind farm, the motions of the particles are simulated. The wake flow effect of velocity decrement is obtained from the density of the particles. On flat terrain, the proposed particle model fits the experimental data better than the previous linear model. On complex terrain, since the particle simulation is based on numerical result of flow field, the particle model can be coupled with optimization algorithm of generating turbine layout. (C) 2011 Elsevier Ltd. All rights reserved.