A backlight assembly, a manufacturing method thereof, and a display device are provided. The backlight assembly includes: a substrate, an anode trace and a cathode trace of an LED on the substrate, a planarization layer on a layer where the anode trace and the cathode trace of the LED are located, and an anode connection pad and a cathode connection pad on the planarization layer. The anode trace of the LED is coupled to the anode connection pad through a first via hole penetrating through the planarization layer, and the cathode trace of the LED is coupled to the cathode connection pad through a second via hole penetrating through the planarization layer. An exhaust channel is further arranged on the planarization layer to discharge gas accumulated in the planarization layer.