Bioplastics are widely used due to their clean raw materials and good degradability. However, the dynamic changes in the physical and chemical properties of materials, especially during photodegradation, as well as the generation mechanism of secondary pollutants and their environmental trends, still lack quantitative evaluation.【Objective】This study investigated the degradation dynamics of three types of bioplastic films (starch based, cellulose based, and polylactic acid based) and a traditional petroleum based polyethylene (PE) film during 0-30 days of light aging, as well as the release of harmful substances such as microplastics and additives, by simulating accelerated degradation experiments under sunlight. 【Result】Scanning electron microscopy (SEM) observed that the density of photo induced cracks on the surface of bioplastic film increased by 2-3 times compared to the initial state after 30 days. Fourier transform infrared spectroscopy (FTIR) showed a 50-80% increase in carbonyl index (CI) (peak intensity significantly increased at 1078 cm ?1), and X-ray diffraction (XRD) analysis showed a 20-35% decrease in crystallinity. The three materials have similar structures, while traditional petroleum based plastics mainly rely on C-C bonds and have relatively weak environmental degradation ability. Quantitative analysis found that among the four materials, starch based biofilm released the highest number of microplastics, reaching more than 7 × 10⁷ pieces. Gas chromatography-mass spectrometry (GC-MS) detection showed the migration of phthalate ester additives (PAEs) in biofilms, among which dioctyl phthalate (DEHP) and dibutyl phthalate (DBP) were released. Although they did not exceed the standard of "Determination of Six Phthalate Compounds in Water Quality by Liquid Chromatography Triple Quadrupole Mass Spectrometry" (HJ 1242-2022), they may still pose environmental risks. 【Conclusion】 Research has shown that although biodegradable films have rapid apparent decomposition characteristics, secondary pollutants such as microplastics, DOM, and PAEs generated during their photodegradation process may form a composite pollution chain, posing a potential threat to soil water ecosystems. It is urgent to strengthen degradation controllability and full lifecycle risk assessment in material design and standard setting.Bioplastics are widely used and researched due to their clean source and good biodegradability.