A wall-mounted air conditioner indoor unit (100), comprising a housing (100), an air outlet channel (140) provided in the housing (110), and an air guide plate (150) configured to be controlled to move horizontally between a second position where the air guide plate (150) moves out of the air outlet channel (140) and a first position where the air guide plate (150) retracts into the air outlet channel (140). The air guide plate (150) comprises an upper plate section (151) and at least one lower plate section (152) connected to the lower part of the upper plate section (151). After the air guide plate (150) moves out of the air outlet channel (140), the air guide plate (150) is configured to be controlled to rotate about the axis parallel to the extension direction of an air outlet so as to adjust the air outlet direction and the air outlet area, so that the air supply diversity and the air supply comfort of the air conditioner indoor unit (100) are improved. Moreover, before moving horizontally from the second position to the first position, the air guide plate (150) is configured to rotate to an initial position where the lower plate section (152) at the bottommost part is aligned with the air outlet, so that the lower plate section (152) at the bottommost part may cover the air outlet when the air guide plate (150) moves horizontally to the first position.