Method, device and system for detecting link state

The invention discloses a method, a device and a system for detecting a link state. The method comprises the following steps: sending a first detection message to a second port of second equipment on an uplink of a first port, wherein, the first detection message comprises an MAC (Media Access Control) address of the first port; judging whether a detection response message is received on a downlink of the first port within preset time; if the detection response message is not received, determining that the link state between the first port and the second port is an optical fiber disconnection state; if the detection response message is received, judging whether the MAC address carried in the detection response message is consistent with the MAC address of the first port or not; if the MAC address carried in the detection response message is consistent with the MAC address of the first port, determining that the link state between the first port and the second port is a normal connection state; and if the MAC