Intersystem EMC database, based on the transmitting parameters and susceptivity, is designed for improving the accuracy of EMC prediction. Structure, content and function requirement of database are described in detail, the layered EMC database design is produced according to the crossindex of all kinds of data, COM technique can guarantee the stable and extension of database in future. Based on the EMC prediction database and coupling calculation of sensitive ports, accurate Intersystem EMC prediction can be realized, which can further improve the development of EMC prediction.