In underwater communication, transmission medium suffer some of the factor like multipath propagation, time varation of channel, limited bandwidth and signal strength attenuation is particularly it as range of long distance. In underwater communication, data rate is low compare to terrestrial communication. However, in underwater communication, acoustic wave is used whereas in terrestrial communication electromagnetic wave is used. There is a need for new advanced signal processing techniques for better underwater communication and networking for developing ocean monitoring and exploration. In this project, we proposed an optimum algorithm to improve the Bit Error Rate (BER) for two different channel conditions in underwater wireless communication using Code Division Multiple Access system (CDMA). The proposed system analyzes the Bit Error Rate (BER) performance of slow fading and fast fading channel using digital modulation scheme like Binary Phase Shift Keying. The performance of BER vs SNR (Signal to noise Ratio) is analyzed for slow fading and fast fading channel using MATLAB software and we find that the proposed system provide better BER.