All optical network based on wavelength division multiplexing transmission system with optical cross connect (OXC) is an essential approach for optical commumications.Crosstalk introduced by OXC (specially large scale one) is a key limiting factor for its capacity. Optical signal passing through a typical OXC is analyzed in this paper, followed by description of the generation and effect of intraband crosstalk.The power penalties induced by intraband crosstalk versus the number of multiplexed wavelengthsMand the number of input fibersNhave been given by numerical simulations. The results show that the coherent crosstalk is the most critical limitation on OXC and depends more closely on the number of multiplexed wavelengths Mthan the number of input fibersN. Crosstalk is suppressed by doubly filtering, fixing optimum decision-threshold and appropriately choosing the number of multiplexed wavelengths M.