Embodiments of the present invention disclose a method, an apparatus and a system for allocating downlink power, which can solve the problem of downlink power allocation under a Coordinated Multi-Point transmitting (CoMP) environment and in a carrier aggregation (CA) technology. The method includes: calculating a power allocation according to measurement parameters which are of a reference signal and are reported by a terminal, and according to the number of physical resources within a measured bandwidth corresponding to each aggregate waveband, and an energy allocated to each resource block on the reference signal corresponding to the each aggregate waveband, where the number of physical resources and the energy are sent by a secondary evolved NodeB (eNB), sending the calculated power allocation to the secondary eNB, and sending to a user equipment (UE) energy information that corresponds to the reference signal corresponding to the each aggregate waveband of the secondary eNB. The present invention is applicable to downlink power allocation.