Proper amount of glass fiber (GF) was added into poly lactic acid (PLA) to improve its mechanical property for adapting to the packing of the products. PLA and GF were mixed together to prepare composite packaging material. In order to enhance the compatibility of the two substances, KH550 was added to modify GF to increase the mechanical properties of the material. And then the mechanical properties, light transmittance, fourier transfer infrared spectroscopy(FTIR)were tested, and the fracture appearance of the composite packing materials was observed by SEM. It was showed that the mechanical properties of the composite packaging material increased after GF was added into PLA. When the mass fraction of GF was 15%, the tensile strength of the composite packing materials reached the maximum. When the mass fraction of the GF was 25%, the impact strength reached the maximum. When the mass fraction of 1% KH550 coupling agent was used to modify GF, the tensile strength increased significantly, because it increased the compatibility between GF and PLA. As the percentage of GF increased, the light transmittance of GF/PLA composite film decreased, whereas the haze increased obviously, thus it influenced the visibility of packaging materials. In conclusion, GF had strong reinforcing effect. It will have significant meaning and wide development in improving brittleness of PLA.