Amethod of data connection by a digital simulator and EMS system is provided in the paper, and integration with off-line data and EMS real-time data can be operated automatically. On present situation, almost all of analyses of electric power system adopt off-line data which is much more onerous input in computer by hand, and the result can not accurately describe the actual condition in operation. With theuse of standard IEC61970 in our country, EMS system has the uniform data-interface. Applying on-line data to playback of system failure, the contrast of oscilloscope data and simulation data demonstrates that on-line data can not only describe the steady characteristic, but also accurately describe transient characteristic of power system. Therefore, researching on EMS data-interface will greatly improve the accuracy of simulation veracity and it will has great significance.