A method and an apparatus for obtaining a precoding matrix indicator is disclosed, which relates to the field of communication technologies. The method includes: obtaining a first rotation matrix according to first channel information; obtaining a first differential matrix according to the first rotation matrix and a currently-obtained instantaneous beam forming matrix/precoding matrix; and quantizing, according to a first differential codebook, a pre-acquired first rank indicator, and preset quantization criteria, the first differential matrix to obtain a differential precoding matrix indicator. The apparatus includes: a first rotation matrix obtaining module, a first differential matrix obtaining module, and a differential precoding matrix indicator obtaining module. The differential PMI is obtained according to the channel information, and the differential PMI is used for feedback.