Provided are a data transmission method and device. The method includes that a terminal sends uplink data in a grant-free manner, detects grant information within a target time window and generates a detection result, the grant information being used for indicating configuration information about a data transmission channel, and the terminal determines, according to the detection result, whether to repeatedly send the uplink data. The embodiments of the present invention facilitate the reduction of a data transmission delay and improve the efficiency, intelligence and stability of data transmission.