Characteristics of Erbium-Doped Fiber Amplifier (EDFA) are studied in this article. Amplification, noise figure and its dependences on different EDFA parameters are simulated and measured in 2.5 Gbit/s one channel transmission system. Also, realization of four 2.5 Gbit/s channel WDM communication system with implemented EDFA line amplifier was inspected in this paper. Almost identical results indicate on high accuracy of simulation. It is shown that the amplification of EDFA depends on various parameters such as signal power, wavelength, EDF length and pump laser configuration.