This application provides a packet processing method and a network device in a hybrid access network, to implement traffic balancing and real-time monitoring on network bandwidth, thereby relieving primary link congestion caused by a network emergency, and improving network bandwidth. The method is: sending, by a first network device, a first data packet in a first sending window to a second network device by using a first tunnel; in response to receiving a first acknowledgement response sent by the second network device, increasing, by the first network device, a size of the first sending window based on a first proportion; in response to not receiving, within a first predetermined time, the first acknowledgement response, decreasing the size of the first sending window based on a second proportion; and in response to determining that the size of the first sending window is greater than or equal to a first threshold, sending a second data packet to a second receiving window of the second network device by using a second sending window, where a first acknowledgement number carried in the first acknowledgement response is obtained based on a first sub-link number in the first data packet.