The invention provides a vertical air conditioner indoor unit which comprises an air supply body, an air supply outlet in the front side of the air supply body is long circular, and the inner wall, close to the air supply outlet, of the air supply body is in a gradually-reduced shape with an overflowing section gradually reduced in the airflow direction. A flow guide piece is arranged on the rearside of the air supply outlet and comprises a front end face, two first flow guide faces and two second flow guide faces, and the two first flow guide faces and the two second flow guide faces extendbackwards from the upper side, the lower side and the two transverse sides of the front end face respectively. The front end face is long-circular. An annular air outlet gap is defined by the flow guide piece and the gradually-shrinking part of the air supply body, the flow guide piece guides airflow to the annular air outlet gap, and the airflow is guided by the inner wall of the air supply bodyto gradually gather towards an airflow center. The first flow guide faces extend from back to front, are gradually far away from the central horizontal symmetric surface of the flow guide piece and each first flow guide face comprise a first concave arc-shaped section and a second convex arc-shaped section which are connected with each other. The second flow guide faces extend from back to front,are gradually far away from the central longitudinal vertical symmetrical surface of the flow guide piece, and each second flow guide face comprises a concave third arc-shaped section, a convex fourtharc-shaped section and a convex fifth arc-shaped section which are connected with one another.