As we know Optical communication Network offers very high potential bandwidth and flexibility. In terms of high bit rate transmission. However, their performance slows down due to some parameter like dispersion, attenuation, scattering. In long haul application, dispersion is the main parameter which needs to be compensated in order to provide better service. Fiber Braggs Grating (FBG) is one of the most widely used element to compensate it, however its performance slows down with the increase in distance. This paper presents an investigation on Pulse distortions due to the third order dispersion (TOD) on very high speed long distance single mode optical fiber communication system using OptiSystem. Presence of the TOD introduces broadening on the propagating pulse. The impact of TOD is observed at the receiving end of transmission line considering the variation of different factors such as transmission reach, bit rate, duty cycle.BER performance are also considered here.