An embodiment of the invention provides a method for acquiring channel state information. The method comprises: a base station sends one or more pieces of downlink signaling to a user equipment, wherein the one or more pieces of downlink signaling instruct the user equipment to feed back channel dimension information, the channel dimension information comprises an effective dimension of a channelsubspace of a statistical channel between the base station and the user equipment, and an effective dimension of the channel subspace is smaller than the number of reference signal ports used for measuring channel state information; and the base station receives the channel dimension information fed back by the user equipment. Because an effective dimension of a channel subspace is smaller than the number of reference channel ports used for measuring channel state information by a user, it is required that a spatial stream used for feeding back the channel state information is smaller comparedwith the prior art, thereby reducing pilot overheads and computation complexity in acquiring the channel state information.