This study focuses on the structural optimization of a composite Vertical Axis Tidal Turbine (VATT) blade designed for low-velocity, shallow-water environments such as those found in Malaysia. Using Finite Element Analysis (FEA), a three-dimensional blade model was developed based on a NACA 0021 profile, incorporating carbon fiber reinforced polymer (CFRP) with a hybrid layup of unidirectional and woven plies. The structural response was analyzed under realistic hydrodynamic pressure derived from tidal current conditions at 5 m/s. A comprehensive parametric study was conducted to evaluate the influence of skin thickness, spar thickness, spar geometry, and number of internal ribs on blade deformation, stress distribution, and mass. Key design positions—including the center rib and ribs near the fixed supports—were held constant, while additional ribs were varied. A Weighted Decision Matrix (WDM) was employed to objectively identify the optimal configuration based on multiple performance criteria. The final optimized design consisted of a 7.5 mm skin, 6.0 mm box-shaped spar, and 10 internal ribs. This configuration yielded a maximum deflection of 0.69 mm, axial stress of 18.13 MPa, transverse stress of 8.86 MPa, and total mass of 29.83 kg—meeting structural performance targets while minimizing weight. The results validate the effectiveness of parametric optimization in improving blade efficiency and support the viability of lightweight composite blades for reliable tidal energy extraction.