This application relates to the field of mobile communications, and in particular, to technologies of obtaining channel state information in a wireless communications system. In a channel information obtaining method, a base station obtains channel state matrix information of some channels based on uplink reference information sent by a terminal and partial channel state information of channels between the base station and the terminal, to obtain channel state matrix information of the channels between the base station and the terminal. Base on this method, relatively complete channel state matrix information of the channels between the base station and the terminal can be obtained. This helps the base station select an appropriate parameter to transmit data to the terminal without causing an additional delay, performance loss, or cost increase, or consuming more time-frequency resources used for the uplink reference signal.