The invention discloses a secondary protection system of a substation. The secondary protection system comprises a press plate, a press plate state acquisition module, a press plate signal processing module, a 485 network and communication management device, a data management device, a network channel module, a dispatching automation master station OPEN-3000 system and a WEB server of the master station system, wherein the press plate state acquisition module is detachably connected onto the press plate, the press plate signal processing module is connected with the press plate state acquisition module and the 485 network and communication management device respectively, the data management device is connected with the 485 network and communication management device and the network channel module respectively, and the dispatching automation master station OPEN-3000 system is connected with the network channel module and the WEB server of the master station system respectively. By the secondary protection system, searching and check can be fulfilled in the dispatching automation master station OPEN-3000 system and are recorded, so that the recording is standard, unified and reliable, remote monitoring and patrol inspection can be carried out, the labor intensity is reduced, patrol inspection which is not in place is prevented, and the working efficiency is improved.