An embodiment of the present invention provides a manufacturing method of an amorphous-silicon flat-panel X-ray sensor; the method reduces the number of mask plates to be used, simplifies the production processes, saves production costs, while also improving the product yield. The manufacturing method comprises: on a substrate, after a gate scan line is formed, forming a data line, a TFT switch element and a photosensitive element through one patterning process, wherein on the mask plate used in the patterning process, a region corresponding to a channel of the TFT switch element is semi-transmissive, whereas regions respectively corresponding to the data line, the photosensitive element and the portion of the TFT switch element other than the channel thereof are non-transmissive; thereafter, on the substrate formed with the TFT switch element and the photosensitive element, a passivation layer and a bias line are formed.