A wall-mounted air conditioner indoor unit, comprising: a housing (100), having an air inlet (101) at the top, an air outlet (102) which faces the lower front portion and extends in a transverse direction being provided at the front side of the bottom; an evaporator (200), provided inside the housing (100) and used for exchanging heat with air flowing from the air inlet (101), so as to form heat exchange air; a fan (300), configured to promote air to flow towards the air outlet (102) from the evaporator (200); a drainage member (600), the length direction of the drainage member being provided to extend transversely below the bottom of the housing (100), and the drainage member and the bottom of the housing (100) defining an air mixing flue (601), allowing indoor air below the housing (100) to flow towards the air outlet (102) through the air mixing flue (601), so as to be mixed with the heat exchange air to form mixed air and then blown towards the indoor; and drainage air deflectors (620, 630), rotatably mounted on the drainage member (600) along a transverse axis and located inside the air mixing flue (601), so as to be controlled to rotate to guide the overflowing area and airflow direction of the air mixing flue (601). Said wall-mounted air conditioner indoor unit can improve comfort of air supply and feeling experience of users, and can also adjust the overflowing area and airflow direction of the air mixing flue, such that air is mixed more uniformly and sufficiently, improving the air mixing effect.