Based on the particle swarm optimization (PSO) algorithm,a novel FWM power estimation method was proposed.And a technique to design the channel frequency allocation in order to minimize the crosstalk due to FWM in optical dense-wavelength-division multiplexing (DWDM) systems was presented.Which is able to support unfixed fiber dispersion parameters along the links and arbitrary span configuration and more than 16 channels frequency allocation.An effective 16 channels allocation method was obtained,and was compared with other similar methods.The result shows that it can restrain FWM effect much more significantly.