The invention discloses a positioning device for an air guide plate of an air conditioner indoor unit shell. The positioning device is composed of a unit shell and the air guide plate. Insertion holes are formed in the left end and the right end of the inner wall of the unit shell correspondingly. A stepping motor is arranged on the left side of the interior of the unit shell. A drive rod and a driven rod are arranged at the left end and the right end of the air guide plate correspondingly. The drive rod and the driven rod penetrate the insertion holes to be arranged. A groove is formed in the left end face of the drive rod and is in a cross shape. The output end of the stepping motor is connected with an air guide plate rotating shaft, and the head portion of the air guide plate rotating shaft is in a cross shape and is exactly inserted in the groove in the drive rod. A limiting plate is arranged on the surface of the air guide plate rotating shaft, a vertical baffle is arranged in the unit shell, and a through hole is formed in the vertical baffle. Two limiting blocks are arranged on the inner wall of the through hole and are perpendicular to each other in position, the air guide plate rotating shaft penetrates the through hole, and the limiting plate is located between the two limiting blocks. By means of the positioning device, the air guide plate rotating shaft and the air guide plate can be connected more tightly, meanwhile, the air guide plate cannot be damaged by positioning of the air guide plate, and the positioning device is worthy of popularization.