Embodiments of the present invention disclose a method and an apparatus for detecting frame types. The method includes: detecting play time of each frame; and if the play time of a current frame is less than the maximum play time of received frames, determining the current frame as a bi-directional predicted frame, B-frame. In the technical solutions provided by the embodiments of the present invention, the frame types are determined according to a coding sequence of various frames and comparison between data amounts of various frames received earlier and later, without decoding a payload. Therefore the impact of a reduction factor is eliminated and the frame types can be detected more accurately.