Based on COMPASS forcefield, the relationship between microstructure and macroscopic properties of poly(propylene-co-gamma-butyrolactone carbonate) (PPCG) was investigated by "Materials Studio" simulation soft successfully for the first time. The results of simulation showed that the molecular chain of PPCG was flexible. Degradable carbonic and carboxylic ester groups were distributed outside the PPCG cell. Furthermore, the structure of microphase separation was observed in PPCG cell. The "Materials Studio" also simulated and calculated the reciprocity between PPCG and caffeine molecule. It was further found that the caffeine molecule was selectively distributed among the segment of carbon dioxide (CO2) rather than the segment of gamma-butyrolactone (GBL). So the microphase separation structure of PPCG can be applied to the self-assembly of drug molecule. And the conclusion offered a theoretical basis for the self-assembly behavior of drug molecule. In a word, the results of molecular simulation not only verified the experimental conclusions, but also showed a clear description of the relationships between molecular structure and macroscopic properties of PPCG. Moreover, it offered a reference for studying the reciprocity between carrier and drug molecule further. (C) 2007 Wiley Periodicals, Inc.