The present disclosure relates to the field of wireless communication technology, in particular to a method, system and device for measuring CSI, so as to solve the problem in the related art where, on the premise that a Massive MIMO technology plays to its strengths, a CSI measurement and feedback mechanism on the basis of a downlink reference signal may lead to obvious time-frequency resource overhead. The method includes steps of: transmitting, by a network side device, a group of reference signals which have been beamformed to a User Equipment (UE), so as to enable the UE to measure the reference signals, each reference signal in the group of reference signals corresponding to a space in a sector; and determining, by the network side device, whether or not a beamforming mode for each reference signal is to be adjusted in accordance with feedback information from the UE. According to the present disclosure, it is able to, on the premise that the Massive MIMO technology plays to its strengths, reduce the time-frequency resource overhead caused by the measurement and feedback of the downlink reference signals.