IEC61850 bring changes to the SAS (substation automation system), the massive hardwired cables are replaced by the high speed process bus. The secondary circuits in substation are simplified significantly. The system integration is done depend on the data model files. At first, the requirements of the testing system for the SAS based on IEC61850 are analyzed. Three types of interoperation testing are provided. The limitations of IEC61850-10 are analyzed. Then a practical testing system for SAS based on IEC61850 is provided in the paper. It is a function oriented testing system. It consists of OMICRON relay testing set, IEC61850 server simulator, IEC61850 client simulator, IEC61850 communication recorder and analyzer. Besides the OMICRON relay testing set, the other devices of the testing system are designed. The testing system can be used in FAT and SAT. At last, the application of testing system is introduced.