Based on the inverse-T and symmetrical independent double-gated (IDG) polycrystal silicon (Poly-Si) nanowire (NW) thin-film transistor (TFT) developed by our group, we investigate and compare the device characteristics operated under single-and double-gate operation modes. Because of the use of an extra-thin Poly-Si NW channel, the electrical potential in the channel is very sensitive to the bias condition of the two independent gates. Consequently, the threshold voltage (V(subscript TH)) and subthreshold swing (S. S.) of the device operated under a single-gate mode are promptly adjusted by the bias applied to the VTH-control gate. When the device is operated under double-gated mode and with large applied drain voltage bias, its output current can been significantly improved due to the elimination of ”early saturation” effect encountered in the single-gated modes. Finally, under a low applied drain voltage, our analysis points out for the first time that the drain current of a device can also be significantly enhanced with the double-gate mode, thanks to the lowering the barrier of carriers.