Performance and service life of flax fiber polymer composites depend on their interfacial adhesive as well as degradation. The interfacial UV ageing of reinforced Polystyrene (PS) composites was examined in this research employing silane modification of flax fibre. Simultaneously, the 3-(Trimethoxysilyl) propyl acrylate, N-[3-(Trimethoxysilyl) propyl] aniline (PAPS), and 3-Amino-triethoxysilane were employed to establish three various levels of intracellular adhesiveness. Tensile tests and surface observations were used to characterize the degradation of the composite. A significant impact on polymer composite UV ageing has been found by using functional groups of silane agents. Aside from their superior interfacial adhesion, APS composites feature less surface whitening, cracks and deterioration in contrast to other materials. There was a 5.3% and 8.0% decrease in fracturing stress and strain when it was aged for eight weeks. Composites with a weak interface adhesion due to aniline and PS matrix incompatibility quickly whiten, shatter, and degrade their constituent parts; as a result. After 8 weeks, aniline's fracture stress had not diminished, despite the fact that aniline absorbs UV rays substantially and may slow down interfacial degradation. As UV light penetrates MPS ester group, it is possible that the interfacial chain slippage will deteriorate. Thus, the fracture stresses of the composites are reduced by a maximum of 35.2%. According to current theories, UV ageing is the outcome of interfacial adhesion and degradation. Plant fibre polymer composites benefit from improved weathering resistance and initial mechanical qualities when modified with an “appropriate” modifier