A thin film transistor and its manufacturing method, an array substrate and its manufacturing method, and a display device are provided. The thin film transistor includes a gate electrode, a source electrode, a drain electrode, an active layer and a gate insulation layer. The gate insulation layer is provided above the active layer, the gate, the source electrode and the drain electrode are provided on a same layer above the gate insulation layer, the active layer and the source electrode are connected through a first connection electrode, and the active layer and the drain electrode are connected through a second connection electrode. The thin film transistor can be formed by three times of patterning processes, by which the process time period is shortened, the process yield is improved, and the process cost is reduced, and so on.