We analyze pulse distortions due to the third- order dispersion (TOD) in ultra- high- speed optical fiber communication by using OptiSystem software. The effects of TOD are observed considering the variation of different factors such as bit rate, duty cycle, pulse shape and fiber type when pulse signals are transmitted through optical fiber communication system at a transmission distance of 2000 km. Meanwhile, we find that Qfactor of Gaussian pulses is better than that of super-Gaussian pulses at a transmission distance of 2000 km. The simulation results show that the performance of a standard single- mode fiber chirped fiber Bragg grating (SSMF-CFBG) system is better in ultra-high-speed application when both group velocity dispersion (GVD) and TOD effects are considered.