Plastic pollution is a major global environmental concern, resulting in increased demands for innovative, green, biodegradable plastics. The work aims to evaluate the degradation behavior of different biodegradable materials in soil environments and to identify key factors influencing their degradation processes. A series of soil burial experiments were conducted to replicate natural soil conditions accurately. The tested materials consisted of starch + polyethylene (PE), polylactic acid (PLA) + poly(butylene adipate-co-terephthalate) (PBAT) + starch, poly(butylene terephthalate) (PBT) + PLA + corn-based substrate, and high-density polyethylene (HDPE) + ECM degradation masterbatch, while PE was used as the control. This study investigated degradation rates, variations in degradation performance, and changes in molecular structure by altering experimental conditions such as burial depth, soil moisture, and soil pH in combination with Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and thermodynamic analysis. The results demonstrated that the crystallinity of the samples significantly influenced their degradation performance. Specifically, the PLA + PBAT + starch sample showed lower maximum mass loss rates and higher peak mass loss temperature, attributed to enhanced intermolecular forces and reduced thermally-induced mobility, leading to improved thermal stability and optimal degradation performance. In conclusion, the samples show optimal thermal stability and degradation performance, providing a robust scientific basis for the development and application of biodegradable plastics, supporting efforts to mitigate plastic pollution.