The invention provides a wide-area message transmission method and a system of a main station and a sub-station, comprising the following steps: a message sender inquires whether a message receiver ison-line through a pre-deployed message management/distribution service; when the message receiver is online, the message sender sends the message to the message receiver in real time. Otherwise, themessage sender sends the message to the message receiver through the message management/distribution service after the message buffer is delayed. The message sender includes a device or an applicationarranged at a primary station or a sub-station to transmit a message, and the message receiver includes a device or an application arranged at the primary station or the sub-station to receive a message. The message sender includes a device or an application arranged at the primary station or the sub-station to transmit a message. The method and the system mainly solve the problems of message transmission and interaction in a wide area such as a substation and a control master station, and adopt a proxy mechanism to construct a message management/distribution service, thereby realizing the maintenance-free access of a message sender and a message receiver, thereby realizing the message communication in a wide area.