The main purpose of this paper is to obtain the gain non-uniformity for each channel in order to equalize the amplitude gain in a WDM (wavelength division multiplexing system). The system is simulated to achieve gain flatness of EDFA (erbium doped fiber amplifier) through optimized fiber length and pump power. The gains are flattened within 24±0.3 dB from 1546 nm to 1558 nm band of wavelength with noise figure (NF) less than 6 dB and bit error rate (BER) less than 10 ^-9 for 16-channels simultaneous amplification in a single stage EDFA. Check the possibility of data can be transmitted with high superiority and less number of errors calculated using SNR and BER equations theoretically.