A method for re-transmitting data applied in a Non-Orthogonal Multiple Access, NOMA, system comprising: determining , by a base station, to re-transmit a data packet after a detection failure message is received from a User Equipment, UE, for a first transmitted data packet that was initially transmitted using the NOMA technique; performing , by the base station, user scheduling, and determining another UE multiplexing a same resource with the UE corresponding to the data packet to be re-transmitted, and generating a user group comprising the UE and the determined another UE; for the UE corresponding to the re-transmitted data packet in the user group, determining, by the base station that the UE is to perform data combination for the data packet when SINR n inTx ≥ α α + 2 SINR n reTx , wherein SINR n inTx denotes a Signal to Interference-Noise Ratio, SINR, of a first-transmitted data packet of the UE, SINR n reTx denotes a SINR of a re-transmitted of the UE, data packet α = h 1 2 h 2 2 , h 1 and h 2 denote a channel transfer function when transmitting the first-transmitted data packet and the re-transmitted data packet for the UE, respectively; calculating a transmission power allocation factor corresponding to each UE in the user group according to a channel quality of each UE in the user group and a determination result whether the UE is to perform the data combination, wherein when it is determined that the UE is to perform data combination, the allocated power for the UE corresponding to the re-transmitted data packet is reduced; and allocating , by the base station, power for a data packet of each UE according to the calculated transmission power allocation factor corresponding to each UE in the user group. determining , by a base station, to re-transmit a data packet after a detection failure message is received from a User Equipment, UE, for a first transmitted data packet that was initially transmitted using the NOMA technique; performing , by the base station, user scheduling, and determining another UE multiplexing a same resource with the UE corresponding to the data packet to be re-transmitted, and generating a user group comprising the UE and the determined another UE; for the UE corresponding to the re-transmitted data packet in the user group, determining, by the base station that the UE is to perform data combination for the data packet when SINR n inTx ≥ α α + 2 SINR n reTx , wherein SINR n inTx denotes a Signal to Interference-Noise Ratio, SINR, of a first-transmitted data packet of the UE, SINR n reTx denotes a SINR of a re-transmitted of the UE, data packet α = h 1 2 h 2 2 , h 1 and h 2 denote a channel transfer function when transmitting the first-transmitted data packet and the re-transmitted data packet for the UE, respectively; calculating a transmission power allocation factor corresponding to each UE in the user group according to a channel quality of each UE in the user group and a determination result whether the UE is to perform the data combination, wherein when it is determined that the UE is to perform data combination, the allocated power for the UE corresponding to the re-transmitted data packet is reduced; and allocating , by the base station, power for a data packet of each UE according to the calculated transmission power allocation factor corresponding to each UE in the user group. <EOS>