The invention relates to an altered-RMB detection method, and device and a storage medium, which comprises the following steps: an image of a banknote under test is acquired, and an area under test and a first contrast area on an image are selected, wherein, in the image of the banknote under test, the gray average of the corresponding image of the altered area is smaller than that of the corresponding image of the normal area, and the gray average of the corresponding image of the first contrast area is larger than the gray average threshold; the characteristic value of the corresponding image of the said first contrast area is calculated and the alteration detection threshold is acquired according to the said characteristic value; the gray average of each pixel of the corresponding imageof the area under test is compared with the said alteration detection threshold, and if the number of the pixels of which the gray average is larger than the said alteration detection threshold is smaller than the set number, the banknote under test is considered to be an altered-RMB. The altered-RMB detection method, and device and the storage medium can identify the altered RMB, so that the usesafety of the financial device can be increased.