A path computation method and a related device are disclosed. The method includes: a second network device receives path requirement information and a recomputation condition that are sent by a first network device; the second network device first obtains by means of computation a path meeting a requirement according to the path requirement information, and sends description information of the path meeting the requirement to the first network device; then the second network device constantly determines whether the recomputation condition is met; and when the recomputation condition is met, the second network device performs path recomputation, and sends description information of a path obtained by means of recomputation to the first network device. Therefore sensitivity for triggering path recomputation can be improved and a quantity of communication messages between network devices can be reduced.