The communication maintenance in smart substation is a tough task when performing secondary work related to MMS, GOOSE and SV frames based on DL/T860. The technical capability of the utilities cannot develop as fast as the manufacturer. Some maintenance difficulties came out in newly-built smart substation. The maintenance work in one bay may affect the function of the whole substation. In some area, the risk of maintenance is not under control of the utilities. Communication simulator is mentioned for the safety of secondary testing work. Running part and testing part of substation is separated physically. No communication error warning will appear due to the use of communication simulator. The risk of secondary maintenance is reduced. In the expansion of the substation, the new bay under construction will communicate with the running part, the use of communication simulator will reduce the effect of the new bay to the substation. The working pressure of the utilities drops dramatically.