A loop detection method and apparatus are provided. The method includes: A first node receives a packet from a second node through a first interface. A node segment identifier is encapsulated at an outer layer of the packet. The node segment identifier identifies a destination node. The first node determines, based on the node segment identifier, that an outbound interface for forwarding the packet is the first interface. The first node determines that a loop exists in a forwarding path of the packet. Whether the loop exists in the forwarding path of the packet is determined by determining whether an interface through which the first node receives the packet is consistent with an outbound interface through which the first node forwards the packet, to further adjust the forwarding path of the packet when the loop exists in the forwarding path of the packet, for example, forward the packet along a backup path or discard the packet, to avoid problems such as port congestion and service packet loss.