The invention discloses an early warning method for a standby channel of a transformer substation. The early warning method is based on a standby channel early warning system comprising a plurality of standby channel early warning devices, a plurality of mobile terminals and a transformer substation control center that are in wireless connection by a GSM (Global System for Mobile Communication) network. The early warning method comprises the steps of initialization: initializing the standby channel early warning devices into initial states and setting parameters into defaults; device self-inspection: allowing the standby channel early warning devices to inspect whether the operating states of the standby channel early warning device meet the set parameters; and short message communication processing: allowing the standby channel early warning devices to acquire remote measurement volume and remote signaling volume and to be communicated with the mobile terminals and the transformer substation control center by a short message mode. The method can detect the situation of a telecontrol channel in real time and reports the operating state to a mobile phone of an operator by the short message mode when the channel has a failure, and the important remote signaling volume can be accessed to the telecontrol channel to ensure that the telecontrol channel serves as the standby channel of the transformer substation.