A thin film transistor (TFT) substrate comprises a substrate, a plurality of pixel electrodes, a gate layer, an active layer, a first source layer and a second source layer, and a drain layer. The pixel electrodes are disposed on the substrate. The gate layer is disposed on the substrate. The active layer is disposed corresponding to the gate layer. The first source layer and the second source layer contact the active layer respectively. The drain layer contacts the active layer and is electrically coupled to one of the pixel electrodes. The gate layer, the active layer, the first source layer and the drain layer constitute a first transistor. The gate layer, the active layer, the second source layer and the drain layer constitute a second transistor. When the first and second transistors are disabled, the first and second source layers are electrically isolated from each other.