A link state packet transmission method and a routing node are disclosed. The method is applied to a tree topology, where the tree topology includes a leaf routing node, an intermediate routing node, and a root routing node. The method includes: receiving, by the intermediate routing node, a link state packet sent by a child routing node of the intermediate routing node; sending, by the intermediate routing node, the link state packet to the root routing node, where the root routing node is configured to aggregate received link state packets to obtain a link state packet set; receiving, by the intermediate routing node, the link state packet set sent by the root routing node; and sending, by the intermediate routing node, the link state packet set to the child routing node of the intermediate routing node.