A thin-film transistor (TFT) and a manufacturing method thereof, an array substrate and a manufacturing method thereof, and a display device are disclosed. The manufacturing method of a TFT includes: forming an active layer, a gate electrode, a source electrode and a drain electrode respectively electrically connected with the active layer, and a gate insulating layer disposed between the gate electrode and the active layer, so that the gate electrode, the source electrode and the drain electrode are formed in the same patterning process. The method can reduce the number of masks used in the manufacturing process of the TFT or an array substrate, reduce the technology process, improve the productivity, and reduce the production cost.