A sensor and its fabrication method are provided, wherein 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 comprising a TFT device and a photodiode sensing device, wherein the TFT device is a top gate TFT. The photodiode sensing device includes: a receiving electrode connected with a source electrode, a photodiode disposed on the receiving electrode, a transparent electrode disposed on the photodiode, and a bias line disposed on and connected with the transparent electrode, the bias line is disposed as parallel to the gate line. In comparison with the conventional technology, the method for fabricating the sensor of the invention 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.