Embodiments of the present invention relate to the communications field, and disclose a data transmission method and device to resolve a problem that a success rate of receiving data by an MTC terminal is relatively low after an SC-PTM technology is introduced. A specific solution is as follows: A base station device sends first control information to a terminal device, where the first control information is used to control repeated transmission of multicast service data; and the base station device sends the multicast service data to the terminal device according to the first control information. The present invention is used in a data transmission process.