The present invention provides a method, a device, and a system for determining a GRE tunnel identifier, applied to a scenario in which there are at least two bonded GRE tunnels between a HAG and HCPE. The method is implemented by the HAG and includes: receiving a service packet that is sent by the HCPE through a first GRE tunnel, where the service packet includes a source IP address of the first GRE tunnel carrying the service packet, and the first GRE tunnel is one of the at least two GRE tunnels; and looking up a correspondence table according to the source IP address of the first GRE tunnel, to determine a tunnel identifier of the first GRE tunnel carrying the service packet, where the correspondence table includes a correspondence between the source IP address of the first GRE tunnel and the tunnel identifier of the first GRE tunnel.