The invention discloses a flat panel detector, a detection method thereof and an X-ray detection device, which are characterized in providing with a data processing unit, a voltage detection unit corresponding to each data line one by one, a switch control unit corresponding to each data line one by one and a signal output unit corresponding to each data line one by one. Through the mutual matching of these units, the short-circuit problem of the flat panel detector can be detected, and the data line with the short-circuit problem is disconnected from the signal output unit, so that in the image recognition stage, when the signal output unit is conducted with the corresponding data line, a second detection voltage is output to an image signal output terminal to make the data line with theshort circuit problem not work in the image recognition stage, thereby the influence of the short circuit on image display can be improved.