The present disclosure discloses a method and device for acquiring channel information, and relates to a massive antenna array transmission technology. The method includes that: a receiving side acquires indexes L of M antennae which send reference signals in N antennae of a sending side; channel information Y between the M antennae and a receiving antenna of the receiving side is acquired; a unitary matrix W with a dimension of N×N is acquired; and an estimate S′ of channel information S between the N antennae of the sending side and the receiving antenna of the receiving side is determined by virtue of the indexes L, the unitary matrix W and the channel information Y.