The present disclosure relates to the field of mobile communications technology. A Method and a device for transmitting data in an unauthorized frequency band are provided. The method includes: determining a starting position of to-be-transmitted data in a radio frame in the unauthorized frequency band; determining position indication information based on the starting position; and transmitting the position indication information, to enable a terminal to obtain the starting position of the to-be-transmitted data in the radio frame in the unauthorized frequency band based on the position indication information.