A thin film transistor (TFT) and manufacturing method thereof, an array substrate and a display device are provided. The thin film transistor comprises a substrate; an active layer formed on the substrate; a first conductive contact layer and a second conductive contact layer formed on the active layer; an etch-stop layer formed over the first contact layer and the second contact layer; and a source connected with the first contact layer, a drain connected with the second contact layer and a gate arranged between the source and the drain formed over the etch-stop layer. The TFT has a simple structure and better performance.