The optical network-on-chip (ONoC) using WDM is the most promising candidate in MPSoCs for their strengths of high communication bandwidth, high energy efficiency, high transmission speed, lower latency and power dissipation. However, when WDM is utilized, new crosstalk noises are introduced, especially the four-wave mixing (FWM) crosstalk noise. In this paper, we propose a general crosstalk noise analysis model for the N-port nonblocking optical router in ONoC using WDM. As a case study, the transmission loss, crosstalk noise, and optical signal-to-noise ratio (OSNR) of the five-, six-port routers with eight wavelengths are presented. The results show the average OSNR is different for the different wavelength signals transmitted in the both routers. For the same channel, the OSNR is different among the signals with different wavelengths. For the same wavelength signal, the OSNR of different channels is also distinct.