A data transmission method and apparatus, a base station, and a user equipment are disclosed. The method includes: obtaining a size and priority information of a first data packet that needs to be transmitted; determining a transmission bandwidth used for transmitting the first data packet; if the transmission bandwidth is less than the size of the first data packet and active packet discarding is allowed according to the priority information of the first data packet, processing the size of the data packet to obtain a second data packet, where a size of the second data packet is less than the transmission bandwidth; and sending the second data packet to a user equipment by using the transmission bandwidth.