The invention discloses a method and device for remotely upgrading PLC (programmable logic controller) firmware. The method for remotely upgrading the PLC firmware comprises the following steps: an upper computer queries whether a PLC needing to upgrade is connected with a cloud server based on ID information of the PLC at the cloud server; the upper computer sends a handshake signal to the PLC needing to upgrade and connected with the cloud server; the upper computer sends a selected upgrade packet to the PLC in successful handshake with the upper computer through the cloud server. The uppercomputer and the PLC are connected to the cloud server, and the corresponding PLC firmware is upgraded on the upper computer according to the ID of the PLC, thereby achieving an aim of remotely upgrading the PLC. Engineering personnel can leave for an industry field without carrying the equipment, and the development cost is saved.