Disclosed in the present invention are a downlink data repeat transmission method and device for addressing a problem in which, when resource mapping is performed in different subframes in a repeat transmission, the numbers of available REs are different, and as a result data cannot be combined when performing repeat transmission of multiple subframes. The method comprises: determining a subframe set of a repeat transmission physical downlink channel; in each subframe of the determined subframe set, and when performing a resource mapping on the physical downlink channel, starting mapping from a specific start character position in a first time slot of the current subframe and mapping to all resources except for a resource corresponding to a reference signal used for demodulation; and transmitting the physical downlink channel according to the resource mapping manner.