The invention discloses an air-conditioner unit air duct system for a vehicle. The air-conditioner unit air duct system comprises a main air supply duct, a first air return duct and a second air return duct. The first air return duct and the second air return duct are arranged on the two sides of the main air supply duct. The main air supply duct is communicated with a compartment. Air-conditioner unit air return inlets communicated with an air-conditioner unit are formed in the first air return duct and the second air return duct. An air-conditioner unit air supply inlet communicated with the air-conditioner unit is formed in the main air supply duct. The air-conditioner unit air duct system further comprises a plurality of air return branch pipes communicated with the first air return duct and the second air return duct. One end of each air return branch pipe is communicated with the first air return duct or the second air return duct, and the other end of each air return branch pipe is communicated with the compartment. It can be seen from the technical scheme that the air return branch pipes are arranged on the first air return duct and the second air return duct and used for dispersing air entering the first air return duct and the second air return duct, return air dispersion is achieved, the resistance of return air inside the first air return duct and the second air return duct is reduced, a pressure head is reduced, the energy consumption of the air-conditioner unit is reduced, and the aim of reducing energy waste is achieved.