Abstract: Polylactic acid (PLA) is widely used in the field of fracture internal fixation because of its excellent performance, but it has the problem of degradation of flexural and shear properties due to rapid degradation rate, so compound modification is one of the ways to improve its performance. In this study, glass fiber (GF) and PLA blended preforms were prepared by the three-dimensional braiding technique, followed by modification of the preforms using coupling agent KH550. The composite materials were prepared using a hot-press molding technique. The composite materials were subjected to in vitro degradation experiments by immersing them in phosphate buffered saline (PBS) solution at 37℃. The results reveal that an increase in GF content leads to a decrease in the quality loss rate and water absorption of the composite. After 28 days of degradation, the crystallinity of samples with 40wt%GF content increases by 12.3% compared to samples with 30wt%GF content. Additionally, the flexural strength decreases by 32.3%, 28.13%, and 16.16% for samples with GF contents of 30wt%, 35wt%, and 40wt%. Similarly, the shear strength decrease by 53.74%, 51.1%, and 47.18% for samples with GF contents of 30wt%, 35wt%, and 40wt%, respectively. This finding indicates that increasing the GF content helps to preserve the mechanical properties of the composite material and alleviate interface damage caused by degradation. The introduction of KH550 resulted in a minimal decrease in the pH value of the degradation medium (PBS buffer solution). After 28 days of degradation, the modified composite material exhibits a decrease in flexural strength of 22.85% and a decrease in shear strength of 56.11%. While combined with SEM images, it is observed that the sample with 30wt%GF content exhibits small fissures on the surface after 7 days of degradation, while significant surface damage is observed after 28 days. In contrast, the sample with 40wt%GF content exhibits less degradation damage, which corroborates the testing results of flexural strength and shear strength. It can be observed that GF promoted the mechanical properties and crystallinity of PLA composites while inhibiting the degradation of PLA. KH550 improved the interface between GF and PLA and had less effect on the pH change of the degradation medium.