High-capacity and long-haul transmission gained great significance in modern communication networks. Optical fiber communication system is good enough to face the high demand of current telecom terrific. This paper will propound the theoretical model showing nonlinear factors which degrade the transmission performances of high-capacity long-haul network. The postulatory model will be validated using simulation of key nonlinear factors such as effective area, launch power, refractive index and fiber length. The transmission performance of the high-capacity long-haul optical network would be analyzed on the basis of some key parameters such as bit error rate and signal-to-noise ratio. Mitigation of nonlinear impairments shows significant impact on transmission performances of high-capacity long-haul optical networks.