This work aimed to solve the problem of the poor mechanical properties of the composites due to the incompatibility of the nano silicon dioxide particles and the poly lactic acid(PLA). Based on the In-situ polymerization principle, the compatibilizer Silica-g-poly lactic acid（SiO2-g-OLLA）of nano silicon dioxide and L-lactic acid was prepared， and then the samples were characterized using FTIR, calorific properties testing, mechanics performance testing， permeability testing and moisture permeability testing. The decomposition temperature of PLLA/SiO2 was higher than PLLA， and its weight loss reached about 74%. The tensile strength of PLLA1/SiO2 film containing 8% SiO2 was nearly equal to that of the film containing 11% SiO2. The values of oxygen permeation and water vapor permeation of PLLA were the lowest, while the values of oxygen permeation and water vapor permeation of PLLA1/SiO2 were the highest. The reaction between L-lactic acid and nano silicon dioxide obeyed the In-situ polymerization principle and the tensile strength of the PLLA1/Si-g-OLLA/SiO2 film was well kept after addition of 11% nano silicon dioxide, and the oxygen permeation and water vapor permeation performance was improved.