Transition matrix, combine with high-resolution transmission electron microscopy (HRTEM) and stereographic projection, was used in this article to predict and characterize the orientations and electron diffraction patterns of b¢¢ precipitates in Al-Mg-Si-(Cu) alloys. It was found that the b¢¢ phases as the main strengthening precipitates had 12 variants with Al matrix, and the orientation relationships could be expressed as (010) b¢¢ //{100} Al , [001] b¢¢ //h310i Al , and [100] b¢¢ // h230i Al . Further, based on the C-centered monoclinic structure of b¢¢ precipitate, a new diffraction patterns model under the [001] Al zone axis could be established, which was in good agreement with the experiment date. Further, it could be used to explain reasonably some issues (for example, the ''cross-shaped'' diffraction streaks phenomenon). Simultaneously, we also found that the b¢¢ precipitates had only three different zone axes, [010] b¢¢ , [304] b¢¢ , and " 106 Â Ã b 00 ; parallel to the [001] Al direction when they were precipitated from the Al matrix, and the b¢¢ precipitate might deviate 1.6 deg from its original orientation because of the lattice relaxation.