A method for downlink transmission in a cloud radio access network for a number of users is applied in a central unit. The central unit determines a specific number of remote radio heads (RRHs) as non-serving RRHs based on a predetermined data compression ratio. For each of many pieces of user equipment (UEs), the central unit determines a combination of RRHs which are non-serving in coordinated multi-point transmission (CoMP) from a plurality of RRHs based on the determined specific number, and then performs CoMP downlink transmission based on the combination of RRHs which are non-serving in the CoMP.