A fabrication method of an active device array substrate is disclosed. A first metal material layer, a gate insulation material layer, a channel material layer, a second metal material layer, and a first photoresist layer are formed over a substrate sequentially. The first photoresist layer is patterned with a multi-tone mask to form a first patterned photoresist layer with two thicknesses. A first and second removing processes are performed sequentially using the first patterned photoresist layer as a mask to form a gate, a gate insulation layer, a channel layer, and a source/drain. The first patterned photoresist layer is removed. A passivation layer and a second patterned photoresist layer are formed over the substrate. A third removing process is performed to form a plurality of contact holes. A pixel electrode material layer is formed over the substrate. The second patterned photoresist layer is lifted off to form a pixel electrode.