Flax fiber cloth and polylactic acid (PLA) were melted and blended to produce PLA/flax non-woven fabric composites through injection molding. The effects of flax fiber addition on the mechanical properties, thermal properties, and degradation performance of composites were explored. The results show that the addition of flax fiber improves the mechanical properties, thermal properties, and energy storage modulus of PLA/flax nonwoven fabric degradable composites, enhances the crystallinity of the composites, and enhances the degradation performance of the composites. When the flax fiber content is 20%, the tensile strength, impact strength, and bending modulus of the composites are 66.0 MPa, 5.52 kJ/m², and 4.0 GPa, respectively. The crystallinity of the composites reaches 13.89%, and the Vicat softening temperature is 141.32 ℃. At the 40 d of degradation, the weight loss rate of the composite with the addition of 20% flax fiber reaches the highest, which is 12.03%. The research results provide data support for the application of PLA/flax fiber composites.