In the course of digital substation construction， there is bound to be a transitional period between the new IEC 61850-based substation automation systems（SAS） and the old ones. To solve the compatibility problem between the new and old systems， a scheme for connecting the conventional intelligent electronic devices to digital substations is proposed， and a communication gateway based on IEC 61850 is designed which includes the configuration tool， protocol converter， data collecting filter and IEC 61850 and OPC server. Moreover， a prototype system based on the above methods is developed and put through testing， demonstrating the validity of the proposed scheme.