A thin film transistor, a controlling method thereof, an array substrate and a display device. The thin film transistor includes: a substrate; and a gate electrode, an active layer, a source and a drain on the substrate. The source comprises two source electrodes electrically connected with each other; the drain comprises two drain electrodes electrically connected with each other, and the two drain electrodes are between the two source electrodes; and the active layer comprises primary channels between adjacent source electrodes and drain electrodes and a secondary channel between the two drain electrodes.