A method for data transmission in multiple carriers performed by a terminal device, the method comprising: • receiving at least one piece of indication information from an access network device, wherein the at least one piece of indication information indicates at least one access control parameter; and • selecting at least one access carrier from at least two candidate carriers based on the at least one access control parameter, wherein the at least two candidate carriers are located in different frequency bands, wherein the at least two candidate carriers comprise at least one first candidate carrier and at least one second candidate carrier, and the at least one access control parameter comprises a threshold of a downlink signal strength, and the threshold corresponds to the at least one first candidate carrier, and the selecting the at least one access carrier from the at least two candidate carriers based on the at least one access control parameter comprises: selecting, from the at least one first candidate carrier, a quantity of those candidate carriers having a downlink signal strength greater than the threshold as the at least one access carrier; and, when the quantity of selected candidate carriers is less than a target quantity, selecting the at least one second candidate carrier as the at least one access carrier. • receiving at least one piece of indication information from an access network device, wherein the at least one piece of indication information indicates at least one access control parameter; and • selecting at least one access carrier from at least two candidate carriers based on the at least one access control parameter, wherein the at least two candidate carriers are located in different frequency bands, wherein the at least two candidate carriers comprise at least one first candidate carrier and at least one second candidate carrier, and the at least one access control parameter comprises a threshold of a downlink signal strength, and the threshold corresponds to the at least one first candidate carrier, and the selecting the at least one access carrier from the at least two candidate carriers based on the at least one access control parameter comprises: selecting, from the at least one first candidate carrier, a quantity of those candidate carriers having a downlink signal strength greater than the threshold as the at least one access carrier; and, when the quantity of selected candidate carriers is less than a target quantity, selecting the at least one second candidate carrier as the at least one access carrier. wherein the at least two candidate carriers comprise at least one first candidate carrier and at least one second candidate carrier, and the at least one access control parameter comprises a threshold of a downlink signal strength, and the threshold corresponds to the at least one first candidate carrier, and the selecting the at least one access carrier from the at least two candidate carriers based on the at least one access control parameter comprises: selecting, from the at least one first candidate carrier, a quantity of those candidate carriers having a downlink signal strength greater than the threshold as the at least one access carrier; and, when the quantity of selected candidate carriers is less than a target quantity, selecting the at least one second candidate carrier as the at least one access carrier. selecting, from the at least one first candidate carrier, a quantity of those candidate carriers having a downlink signal strength greater than the threshold as the at least one access carrier; and, when the quantity of selected candidate carriers is less than a target quantity, selecting the at least one second candidate carrier as the at least one access carrier.