Provided herein is a mask inspection device, including an inspection base, a shift platform, a rotating platform, a bearing platform, a laser ranging module, a vertical shift module, a processing module, and an image capturing module. A mask, which is carried and held by the bearing platform, includes a dust-proof film, each region of which is measured by the laser ranging module for generating a distance measuring signal; each distance measuring signal is utilized to control the movement of the vertical shift module, such that image capturing module can take an inspection image of that region. Based on the distance measuring signals and inspection images, height information of the dust-proof film and inspection information can be acquired. Also provided herein is a method applicable to said mask inspection device.