The influence of IP bursty traffic on combined nonlinear effects of cross phase modulation (XPM) and four-wave mixing (FWM) in IP over WDM networks is investigated by analyzing the Poisson distributed IP traffic based on the nonlinear Schrdinger equation (NLSE). Taken combined nonlinear effects into account,at the receiver,different eye diagrams with different input light powers and different IP traffic loads are obtained. From the numerical calculation results,when the input light power per channel is bigger than 5 dBm with 40 channels of WDM networks,the effect of IP bursty traffic will distort eye diagrams drastically. Furthermore we figure out the FWM power with different IP traffic loads,different input light powers and frequency spacings. FWM power with different wavelength settings is especially emphasized. From the FWM power distribution,we could quantitatively analyze which channels cross the probe channel seriously through FWM effect.