The communications under the shallow water are affected by the impulsive components of the ambient noise, in which its statistics does not follow the normal Gaussian distribution. Since most of the communication receivers are designed to receive the Gaussian noise signals, its Performance degrade in the presence of non-Gaussian noise. The noise with Gaussian Mixture (GM) distribution can be considered as one of the most popular non-Gaussian noise that is used to model the UWA, due to its universal approximation properties. However, there were a little researches investigate and present an analytical analysis of the spread spectrum error probability in the UWA with the GM noise. In this paper, the
traditional Chaotic Sequence Code (CSC) is applied and verified as a spreading code for UWA channel with GM noise. The error performance is presented and derived analytically with and without the spreading process. The results show that applying the CSC significantly improves the performance in the UWA with the GM noise.