Disclosed is a testing system, which includes a thin film transistor substrate. The thin film transistor substrate includes a plurality of thin film transistors and a plurality of connecting pads. Each of the thin film transistors includes a first electrode, a second electrode, and a third electrode. The thin film transistor substrate further includes a testing pad. One of the first electrode and the second electrode of each of the thin film transistors is electrically connected with one of the connecting pads. The third electrode and the other one of the first electrode and the second electrode of each of the thin film transistors are electrically connected with the testing pad. The testing system of the present invention is capable of decreasing the cost of the testing system and the complexity of disposed circuits.