An array substrate, manufacturing method thereof and a display device are provided. The array substrate comprises thin film transistor units (2) arranged in array, and further comprises a quantum dot layer (3) disposed over the thin film transistor units (2). The quantum dot layer includes at least three kinds of quantum dots, any one kind of which emits light of a respective wave band when being irradiated and excited by light from an incident portion of the array substrate. The array substrate can improve color gamut range, transmittance of a display device without increasing the power consumption of the display device.