A method for determining a transmission buffer size, including acquiring a transmission delay of a data packet that is sent by a transmit end on a transmission link between the transmit end and a receive end, updating a minimum transmission delay according to the transmission delay and based on a first update period when a primary congestion status of the transmission link is congested, updating the minimum transmission delay according to the transmission delay and based on a second update period when the primary congestion status is non-congested, where a period length of the first update period is shorter than a period length of the second update period, obtaining a minimum transmission delay of the transmission link, and determining a transmission buffer size of the transmission link according to the transmission delay and the minimum transmission delay.