The invention discloses a traceability relation establishing method and a device thereof, wherein the traceability relation establishing method comprises the steps of: receiving a dynamic host configuration protocol (DHCP) message from a cable modem (CM) by aggregation forwarding equipment; and establishing a traceability relation between the DHCP message and the CM according to preset index information by the aggregation forwarding equipment. The traceability relation establishing method realizes an effect of interpolating relay agent information Option82 into the DHCP message which is forwarded to the aggregation forwarding equipment according to an Ethernet protocol after transmitting through a cable media converter (CMC).