The present disclosure relates to methods for feeding back channel state information, user equipment, and base stations. One example method includes receiving a reference signal sent by a base station, selecting a precoding matrix W from a codebook according to the reference signal, where a column vector of the precoding matrix W is expressed as α[v ejϕv]T, v=[1 ejθ], and sending a precoding matrix indicator (PMI) to the base station, where the PMI corresponds to the selected precoding matrix W.