The invention discloses a shutter, a shutter assembly, an air conditioner indoor unit and an air conditioner, in the length direction of the shutter, the shutter has a first end and a second end opposite to the first end, the first end is suitable for connection with the air conditioner indoor unit, and one side, partially facing to the thickness direction of the shutter, of the second end bends to form a bending part. According to the shutter, one side, partially facing to the thickness direction of the shutter, of the second end bends to form the bending part, when the shutter swings to sweep, air flow disturbance can be enhanced, the air flows can be scattered favorably, the air flow speeds are reduced, a lot of concentrated height air flows can be prevented from blowing to the user directly, and the user's comfort is increased. Besides, when the shutter swings up and down, the bending part bends downwards, partial air flows can be pressed lower during heating, the heating comfort is improved, partial air flows can flow upwards during refrigeration, and the refrigeration comfort is ensured.