The Dense Wavelength Division Multiplexing offers the transmission of multiple streams simultaneously. For long haul communications, it is required to amplify the signal for the effective transmission. In a DWDM communication network usually EDFA is used for the amplification purpose since it offers low cost and more than that its ability to amplify multiple signals at the same time. However, there are several factors which affects the transmission of a signal and is called as the fiber nonlinearities. The important non-linearity factors are Amplified Spontaneous Emission, Four Wave Mixing and Polarization Mode Dispersion. This paper analyzes the nonlinearities affecting a DWDM communication network.