Many researchers are searching for structural materials of high strength, less weight, and low cost. In generally, strong materials are relatively dense and light materials have less strength. In order to achieve high strength and less weight, we go for composite materials. Then the tensile strength and impact strength of specimens are determined using ultimate testing machine and impact testing machine. The structure of an autonomous underwater vehicle (AUV), usually composed of a cylindrical shell, may be exposed to high hydrostatic pressures where buckling collapse occurs before yield stress failure. In conventional submarines, welded stiffeners increase the buckling resistance, however, in small AUVs; they reduce the inner space and cause residual stresses. This study investigates the mechanical properties of composite materials by incorporating various fibers, namely E-glass, Kevlar and Carbon fiber, each combined with a 10% addition of graphite powder. Additionally, hybrid combinations of these fibers such as E-glass + Kevlar + 10% graphite powder, Kevlar + Carbon fiber + 10% graphite powder, Carbon fiber + E-glass + 10% graphite powder and Carbon fiber + E-glass + Kevlar + 10% graphite powder are explored. Polyester-resin is utilized as the matrix material to form the composite specimens, adhering to ASTM standards. The research focuses on evaluating the mechanical performance of the composite materials through comprehensive testing methods: tensile strength, flexural strength, impact strength. After that design of an AUV pressure vessel, proposing the use of sliding stiffeners that are part of the structure used to accommodate the electronics inside it. Design of AUV pressure vessel using CATIA software and analysis using ANSYS software using two materials existing AL 6061 and after best composite material. I.INTRODUCTION: Keywords: E-glass, Kevlar and Carbon fiber, resin, AUV, Pressure, composite material