A data transmission method in a communications network, the communications network comprising a source access network device and a target access network device, the source access network device and the target access network device configured to perform a handover operation for handing over a terminal device from the source access network device to the target access network device using a split bearer, the method comprising: sending to the terminal device, by the source access network device or the target access network device, a sequence of first-type packets enciphered by the source access network device using a first cipher key; and after sending, by the source access network device or the target access network device, the sequence of first-type packets, sending, by the source access network device or the target access network device, a sequence of second-type packets enciphered by the target access network device using a second cipher key; wherein the method further comprises: sending, by the source access network device and/or the target access network device, first indication information to the terminal device, wherein when sent by the source access network device, the first indication information is used to indicate a last packet in the sequence of first-type packets and when sent by the target access network device, the first indication information is used to indicate a first packet in the sequence of second-type packets; wherein the first indication information is carried in a data protocol data unit; and the data protocol data unit further carries third indication information, the third indication information is used to indicate that the first indication information is carried in the data protocol data unit, and a sequence number of the data protocol data unit is a sequence number indicated by the first indication information; sending to the terminal device, by the source access network device or the target access network device, a sequence of first-type packets enciphered by the source access network device using a first cipher key; and after sending, by the source access network device or the target access network device, the sequence of first-type packets, sending, by the source access network device or the target access network device, a sequence of second-type packets enciphered by the target access network device using a second cipher key; wherein the method further comprises: sending, by the source access network device and/or the target access network device, first indication information to the terminal device, wherein when sent by the source access network device, the first indication information is used to indicate a last packet in the sequence of first-type packets and when sent by the target access network device, the first indication information is used to indicate a first packet in the sequence of second-type packets; wherein the first indication information is carried in a data protocol data unit; and the data protocol data unit further carries third indication information, the third indication information is used to indicate that the first indication information is carried in the data protocol data unit, and a sequence number of the data protocol data unit is a sequence number indicated by the first indication information; sending, by the source access network device and/or the target access network device, first indication information to the terminal device, wherein when sent by the source access network device, the first indication information is used to indicate a last packet in the sequence of first-type packets and when sent by the target access network device, the first indication information is used to indicate a first packet in the sequence of second-type packets; wherein the first indication information is carried in a data protocol data unit; and the data protocol data unit further carries third indication information, the third indication information is used to indicate that the first indication information is carried in the data protocol data unit, and a sequence number of the data protocol data unit is a sequence number indicated by the first indication information;