An optical system with specification of eight channels, 10 Gbps as bit rate, differential phase shift keying (DPSK) as a modulation format and 300 Km optical fiber length that consist of five spans each with 60 Km containing dispersion compensating fiber (DCF) and Erbium doped fiber amplifier (EDFA) have been studied. It is in the form of bit error rate (BER) Vs Signal-to-noise ratio (SNR) and quality (Q)-Factor Vs input power (P) for different channel spacing (200, 100, 50 and 25 GHz). The result pointed that the spacing between channels of 200 GHz was the best because the BER has been improved by (2 orders) if it compared with the 100 GHz channel spacing system at 10 dB SNR, the BER in the case of channel spacing 100 GHz also improved by ( 1.9 orders) if it compared with the 50 GHz channel spacing system at 10 dB SNR and the BER also improved by ( 0.7 orders) in the case of optical systems with 50 GHz as if we compared it with system of 25 GHz channel spacing at 10 dB SNR. The Q-Factor has been improved as the channel spacing increased, so generally the performance of an optical fiber system has been improved with the presence of DCF and EDFA in the optical link because the effect of these two elements in the linear and nonlinear fiber impairments.