The present disclosure provides an organic transistor and a manufacturing method thereof, an array substrate, and a display device. The method for manufacturing the organic transistor includes: applying a photoresist on a side of an organic insulating layer; patterning the photoresist to form a confinement well; adding a solution of an organic semiconductor material and an orthogonal solvent to the confinement well; volatilizing the orthogonal solvent by an annealing process to induce directional growth of single crystal of the organic semiconductor material in the confinement well, thereby obtaining an organic single crystal layer; and removing remaining photoresist and using the organic single crystal layer as an active layer. The embodiment of the present disclosure produces an organic single crystal in a flexible display device at a low temperature, and the organic single crystal can be used as an active layer, resulting in an organic transistor having high mobility and stability.