The invention discloses a real-time diagnosis device and method for thermal power plant equipment cavitation. The device comprises a cavitation diagnosis client connected to a thermal power plant MIS network through an Ethernet interface, a remote cavitation diagnosis client I and a remote cavitation diagnosis client II, wherein a cavitation diagnosis server accesses the thermal power plant MIS network through a second Ethernet interface of the cavitation diagnosis server and is connected with an Ethernet switch through a first Ethernet interface of the cavitation diagnosis server; a first data acquisition interface machine is connected with a first firewall through a first Ethernet interface of the first data acquisition interface machine and connected with a first OPC server through a second Ethernet interface of the first data acquisition interface machine, and the first firewall is connected with the Ethernet switch; a second data acquisition interface machine is connected with a second firewall through a first Ethernet interface of the second data acquisition interface machine and connected with a second OPC server through a second Ethernet interface of the second data acquisition interface machine, and the second firewall is connected with the Ethernet switch. The real-time diagnosis device is simple in structure, high in real-time property, accurate in diagnosis, high in efficiency and high in safety and reliability, is isolated with a power plant control system through hardware and can meet the requirement for safety operation of the thermal power plant.