The utility model discloses an ultra -thin cabinet lamp's side light emitting structure, including light guide plate, diffuser plate, LED light source plate, the backplate ring of kneading dough, the face ring is the rectangle framework, the backplate seals the inboard of face ring to the table side that makes the face ring forms the light -emitting portion of stepping down, diffuser plate and light guide plate install in proper order in the interior table side of face ring, LED light source plate install in the side of face ring to middle part to the face ring is luminous, and makes light loop through diffuser plate, light guide plate and the light -emitting portion of stepping down. The utility model provides an ultra -thin cabinet lamp's side light emitting structure has greatly improved the illuminating effect, has eliminated the granular sensation of light source, makes the illumination more even.