The　serrated　yielding　in　metals　and　alloys　is　an　important　and　interesting　physical　phenomenon.　No.　3004　aluminum　alloy　has　been　subjected　to　tension　test　in　a　range　of　strain　rates　5.56　×　10-5　s-1　-　5.56　×　10-3　s-1　and　temperatures　223　K-773　K　to　investigate　the　ordinary　rules　of　serrated　yielding　phenomenon.　The　micro-mechanism　and　physical　essence　of　serrated　yielding　of　the　material　have　been　studied　by　means　of　activation　energy,　internal　friction　and　microstructure.　The　results　show　that　the　serrated　yielding　phenomenon　is　associated　with　the　dynamic　strain　aging　process.　In　the　serrated　yielding　temperature　region,　an　anomalous　serrated　yielding　phenomenon　was　found.　Within　this　temperature　region,　a　critical　transition　temperature　Tt　exists.　The　critical　plastic　strain　for　the　onset　of　serrations　has　a　negative　or　positive　temperature　coefficient　within　the　temperature　region　lower　or　higher　than　Tt,　respectively.　The　former　is　the　normal　serrated　yielding　and　the　latter　is　called　＇anomalous＇.　It　is　believed　that　the　process　at　the　temperature　region　lower　than　Tt　is　controlled　by　the　interaction　between　Mg　solute　atom　atmosphere　and　dislocations.　In　the　positive　coefficient　region,　the　aggregation　of　Mg　atoms　and　the　precipitation　of　second　phase　decrease　the　effective　amount　of　Mg　atoms　in　solid　solution　and　lead　to　the　appearance　of　a　positive　temperature　coefficient　of　the　critical　plastic　strain　for　the　onset　of　serrations.