Directed　Energy　Deposition　(DED),　a　branch　of　AM　processes,　has　emerged　as　a　significant　technique　for　fabricating　large　metal　components　in　sectors　such　as　aerospace,　automotive,　and　healthcare.　DED　is　characterized　by　its　high　deposition　rate　and　scalability,　which　stand　out　among　other　AM　processes.　However,　it　encounters　critical　issues　such　as　residual　stresses,　distortion,　porosity,　and　rough　surfaces　resulting　from　rapid　melting　and　solidification.　As　a　novel　advancement,　Ultrasonic-Assisted　Directed　Energy　Deposition　(UA-DED)　integrates　ultrasonic　oscillations　into　DED　aimed　at　addressing　these　challenges.　Herein,　the　latest　research　related　to　the　UA-DED　process　and　the　current　major　challenges　of　the　DED　process,　residual　stresses,　porosity,　and　crack　defects　are　critically　reviewed.　Subsequently,　the　paper　also　details　the　working　principle　and　system　components　of　UA-DED　technology　and　reviews　the　material　improvement　by　introducing　UA　into　the　DED　process,　grain,　porosity,　tensile　properties,　and　deposition　defects.　The　most　critical　optimization　methods　of　process　parameter　variables　for　UA　and　the　different　material　interaction　mechanisms　between　UA　and　DED　processes　are　identified　and　discussed　in　detail.　Finally,　the　perspectives　on　the　research　gap　and　potential　future　developments　in　UA-DED　are　also　discussed.