Abstract: The PLLA (L-polylactic acid) film with porous structure at the surface were fabricated by casting solution technique without the extra-component besides the solvent and solute. The low-molecular weight polylactic acid was mixed with the high-molecular weight polytactic acid and its influence on the properties and strucure of polylactic acid membrane were researched by scanning electron microscopy, differential scanning calorinetry and mechanical test machine. The addition of low-molecular weight PLLA results in porous structure at the surface of the membrane as we expected, in the meanwhile it can also meet the requirmentssuch as adequate mechanical properties for the clinical application and good biocompatibility. This process simplifies the influence on the properties of membrane.