A TFT flat sensor comprises pixel units each comprising: a common electrode and a common electrode insulating layer on a substrate, wherein a first via hole is provided in the common electrode insulating layer at a location corresponding to the common electrode; a gate electrode on the common electrode insulating layer; a first conductive film layer on the common electrode and the gate electrode wherein the first conductive film layer contacts the common electrode through a first via hole; a gate insulating layer, an active layer, a drain electrode and a source electrode, a second conductive film layer, a protection layer and a third conductive film layer on the first conductive film layer; a second via hole is provided in the protection layer at a location corresponding to the source electrode through which the third conductive film layer contacts the source electrode.