Embodiments of the present disclosure provide a data transmission method and apparatus. The method includes: receiving, by user equipment UE, first synchronization source configuration information on a first carrier; determining, a first synchronization source based on the first synchronization source configuration information; determining that synchronization with the first synchronization source fails; determining a second synchronization source and a transmission resource; and transmitting data on a second carrier using the determined transmission resource and based on the second synchronization source, where the first synchronization source is used to provide the UE with a synchronization clock required for transmitting the data on the second carrier, and a frequency of the first carrier is different from a frequency of the second carrier.