Bioplastics reinforced with natural fibers are gaining attention for their potential in various emerging eco-friendly applications, resulting in new materials with exceptional mechanical and thermal properties. This study examines PHA biopolymer plastic as a polymer matrix for natural fibers, specifically date palm, coconut, and sisal. It focuses on calculating shear damage at the fiber-matrix interface for the biocomposites date palm/PHAs, coconut/PHAs, and sisal/PHAs. The results show that under mechanical stresses (σ = 40, 45, 50, and 55 MPa), damage levels increase due to the accumulation of stresses, with sisal/PHAs exhibiting more severe degradation at the interface compared to date palm/PHAs and coconut/PHAs. These findings highlight the significant role of natural fibers in enhancing the mechanical properties of composite materials.