Embodiments of the present disclosure provide a method for obtaining channel state information, including: sending, by a base station, one or multiple pieces of downlink signaling to user equipment, where the one or multiple pieces of downlink signaling instruct the user equipment to feed back channel dimension information, where the channel dimension information includes an effective dimension of a channel subspace of a statistical channel between the base station and the user equipment, and the effective dimension of the channel subspace is less than a quantity of reference signal ports used to measure channel state information; and receiving, by the base station, the channel dimension information fed back by the user equipment.