The substation time synchronization system is the infrastructure of a power system. It is an important basic condition for power system operation control and fault analysis. At present, in the time synchronization system running in the field, some of the slave stations do not have the time synchronization online monitoring function, and some of the time synchronization online monitoring is only implemented in the slave station, and so online monitoring of the entire network cannot be performed. In order to orient time synchronization monitoring of the whole network, an overall solution for time synchronization monitoring between the main station and the substation is proposed. The system architecture of time synchronization monitoring between the main substation and the substation is designed, and the key technologies involved are analyzed, including unified information modeling, time synchronization monitoring system application functions and testing techniques. At present, the time synchronization online monitoring system based on the unified information model has been running stably in the Jiangsu Power Grid. This work is supported by National Natural Science Foundation of China (No. 61602251) and Science and Technology Project of State Grid Jiangsu Electric Power Co., Ltd. (No. J2019038).