A scanning chassis is suited for scanning a document. The scanning chassis includes a case, a light source, at least one reflector, a lens assembly and an optical sensor. The case has a light transparent slot shaped like a bar form, wherein the widths corresponding to the points along the longitudinal direction of the light transparent slot are not all the same. The light source can illuminate the document and an image can be generated at the place where the document is illuminated by the light source. The image can be projected on the reflector through the light transparent slot. The image can be projected on the lens assembly by the reflector's reflecting the image. The image can be projected on the optical sensor after the image passes through the lens assembly.