Today’s TFT LCD Panel Makers use optical measurement to measure the distance of patterns exposed by two different masks to present the alignment accuracy of two mask . But it is hard to do a lot of alignment accuracy check,because the optical measurement’s tact time is very long for each inspection . This article mainly introduced the method for checking alignment accuracy of a thin film transistor (TFT),the switch is using the Mask Overlap relations to form a open or non-open circuit and combine the Array TEG(Test Element Group) for checking alignment accuracy. It was found the design of space GE/PE should be 3.5um,because after wet etching process it will become to 2um,it means that the overlap of GE/PE is almost about 1um,will match the control spec of Overlap for LCD Maker.