A detecting method and a detecting device for a display panel are provided. The detecting method includes: collecting a first detection image of the display panel, and acquiring a gray scale value of each of pixel elements in the first detection image; determining the pixel element of the first detection image having the gray scale value outside a default gray scale range as a first pixel element, determining a first communication region constituted by each of the first pixel element of the first detection image, and calculating an aspect ratio of the first communication region; and looking up a target parameter matching with the aspect ratio of the first communication region from a pre-built database, and determining a target type corresponding to the target parameter as a type of the display panel.