The invention relates to an online monitoring communication method from a substation sub station to a main station. The method comprises the steps that after ICD file unified configuration, a whole station online monitoring information model is formed and is mapped into a real-time data model library; after communication driver loading, an IEC61850 report writing control block service is provided; the function of online monitoring data reporting of a substation sub station is completed; an IEC61850 main station program of the main station acquires online monitoring data by periodically calling a report reading control block service function; the data are parsed by a parse service of an online monitoring equipment model and are stored into the real-time model library according to a certain structure; and a memory data management program provides a data interface for an SCADA monitoring system, so that the online monitoring data are displayed in real time in the SCADA system. The method uses the latest IEC61850 specification of the international standard, has the characteristic of interconnection, and greatly improves the flexibility, the scalability and the maintainability of the online monitoring system.