A downlink channel estimation method and apparatus based on a sounding reference signal (SRS), and a communications system. The method includes: a base station receives a SRS sent by UE, the SRS being used for downlink channel estimation and supporting high-dimensional MU-MIMO; performing uplink channel estimation according to the SRS; and acquiring downlink channel information according to uplink channel information obtained in the uplink channel estimation. By means of embodiments of the present disclosure, downlink reference signal overheads and feedback overheads can be remarkably reduced, gain brought by large-scale antennas is obtained, and the system capacity can be further improved.