The utility model relates to an underground high-voltage power tunnel water level online monitoring device, and belongs to the technical field of power monitoring equipment. According to the technical scheme, an upper computer (1), monitoring hosts (2), water level monitoring devices (3) and water level probes (14) are sequentially connected from top to bottom, the number of the monitoring hosts is one or more, the number of the water level monitoring devices connected with each monitoring host is more than one, the number of the water level probes connected with each water level monitoring device is more than one, the upper computer and the monitoring hosts are connected through TCP/IP Ethernet interfaces, and the monitoring hosts and the water level monitoring devices are connected through a pair of low-smoke halogen-free flame-retardant communication cables. The underground high-voltage power tunnel water level online monitoring device has the advantages that by means of the device, online monitoring of the water level of an underground high-voltage power tunnel can be achieved, meanwhile, water level states of the tunnel can be accurately reported, pre-warning is achieved, intervention can be carried out in advance, and situations can be handled in time. The system is high in pertinency, good in reliability and fully functional.