The invention relates to a thin film transistor and a manufacturing method of the thin film transistor. The thin film transistor comprises a base plate, a first grid electrode, an insulating layer, an active layer, a source electrode, a drain electrode and a second grid electrode, wherein the base plate, the first grid electrode, the insulating layer, the active layer, the source electrode, the drain electrode and the second grid electrode are arranged in sequence. A back channel trench area is arranged between the source electrode and the drain electrode, and the second grid electrode is formed in the back channel trench area. According to the thin film transistor and the manufacturing method of the thin film transistor, a layer of the second grid electrode is additionally arranged in the back channel trench area. A floating gate structure is adopted to control charge distribution in the back channel trench area, and thereby a threshold voltage of a device is adjusted. The threshold voltage of the thin film transistor device is reduced, and a low-power-consumption oxide thin film oxide display device is achieved. The stability of the device is improved, and the manufacturing cost of the device is lowered.