Indoor unit of air conditioner

The utility model provides an indoor unit of an air conditioner. The indoor unit of the air conditioner comprises a machine shell, a fresh air duct and an anti-backflow unit, wherein the fresh air duct is formed in the machine shell and communicated with the interior of a room, and one end of the fresh air duct is connected with a fresh air pipe; the anti-backflow unit comprises an outer cylinder and an inner inserting pipe, wherein a first end cover and a second end cover are arranged at the two opposite ends of the outer cylinder correspondingly, and the inner inserting pipe communicates with the fresh air pipe. The outer cylinder, the first end cover and the second end cover jointly define a cavity; a first air inlet is formed in the first end cover, and a second air inlet is formed in the second end cover; two partition plates distributed at intervals are arranged in the cavity, and the cavity is divided into a first air cavity, a second air cavity and a third air cavity which are distributed in the direc