Embodiments of this application provide a period mapping method and a network device. The method includes: receiving, by a downstream first network device, first information sent by an upstream second network device, where the first information carries a number of the 1st period of the second network device, the number is referred to as a first number, and the first number includes a first label number and a first group number; and establishing, by the first network device, mapping relationships between numbers of a plurality of periods of the first network device and numbers of a plurality of periods of the second network device based on a mapping relationship between a second label number and a second group number that are included in a number of a first period that can be used to send the first information and a first label number and a first group number.