A sensor and its fabrication method are provided, the sensor includes: a base substrate, a group of gate lines and a group of data lines arranged as crossing each other, and a plurality of sensing elements arranged in an array and defined by the group of gate lines and the group of data lines, each sensing element including a TFT device and a photodiode sensing device, wherein a channel region of the TFT device is inverted and the source and drain electrodes are positioned between the active layer and the gate electrode. The sensor reduces the number of mask as well as the production cost and simplifies the production process, thereby significantly improves the production capacity and the defect-free rate.