The invention discloses a method and a device for downlink cooperative retransmission of a relay station. The method comprises the following steps that: the relay station performs physical layer processing on data needing to be retransmitted in advance according to various undetermined conditions of the number of available wireless resources of retransmission data on a retransmission subframe, generates corresponding orthogonal frequency division multiplexing (OFDM) signals and monitors the physical control format indicator channel (PCFICH) of the retransmission subframe; and the relay station selects the OFDM signals with the number matched with that of the determined available wireless resources from the OFDM signals to perform retransmission according to the monitoring result. The method and the device have the advantages of effectively solving the problem that cooperative communication of the relay station cannot be normally performed because the number of the wireless resources changes during downlink data retransmission, along with no additional expenses or time delay.