To eliminate the release-delayed phenomenon of macromolecular drug delivery system at the early stage, biodegradable implantable drug delivery system with micro-porous structure was designed by Bio-MEMS technology in this paper. Water absorption and degradation characters of polylactic acid - polyglycolic acid (PLGA) material with different monomer ratio were studied. Drug release model was built by mass transfer equation and the Finite Element Method. Influencing factors about the cumulative amount of release drug were analyzed. And the results suggest that with more ratio of polylactic acid(PLA), PLGA would have more greater amount of water absorbed as well as a longer degradation time. Better linearity of cumulative amount of release drug would be achieved by reducing the diameter and number of micro-porous.