A network device adds a fixed value to a congestion threshold (CT) when a first period ends. Detects whether a difference obtained by subtracting average traffic load of a queue in the first period from average traffic load of the queue in a second period is greater than a target increase value, sets the CT based on a detection result when the second period ends, where the first period is previous to the second period; marks a received packet when a quantity of packets buffered in the queue is greater than the CT, enqueues the marked packet and sends the marked packet to a receiving device.