Disclosed are a manufacturing method of an array substrate, an array substrate and a display device. The manufacturing method of the array substrate includes: providing a substrate; depositing and patterning a gate layer on the substrate; depositing a protective layer on the substrate covered with the gate layer by atomic layer deposition; and depositing and patterning an amorphous silicon layer and an ohmic contact layer on the protective layer. The uniform protective layer of the present disclosure reduces the influence on the field effect mobility of the thin film transistor, makes the display of the product more stable, and improves the display effect.