Nowadays, the long-haul optical fiber communication system is one of the important way to convey the information, and there is strong competition of research in the optical long-haul transmission to achieve high channel bit rates and large transmission capacity. Therefore, it is important to study a technology to improve the performance of such system. The return-to-zero differential phase-shift keying (RZ-DPSK) and the return-to-zero differential quadrature phase-shift keying (RZ-DQPSK) have received renewed attention recently for the long-haul transmission systems, because they can improve the transmission performance of the long-haul system. Furthermore, the design of the dispersion map becomes significantly different from that of the conventional system using the intensity modulation direct detection (IM-DD) scheme. Besides, the RZ-DQPSK can transmit two bits per symbol, so it has twice the spectral efficiency of the RZ-DPSK. This study is focusing on the difference of the transmission performance of the long-haul RZ-DQPSK system due to the dispersion map using the numerical simulation.