A packet transmission method and apparatus, and a system. The method includes: after receiving a first packet, a first device determines, based on a condition met by a first number carried in the first packet, a manner of sending the first packet. When the first number of the first packet meets a first condition, a second device determines a second cycle label corresponding to a first cycle label and sends the first packet to a third device in a cycle corresponding to the second cycle label. When the first number of the first packet meets a second condition, the second device determines a third cycle label corresponding to the first cycle label and sends the first packet to the third device in a cycle corresponding to the third cycle label.