The invention relates to a method for extracting a document image by a pick-up device. The method comprises the following steps of: mounting a laptop computer; providing a document fixer; placing a document in the document fixer in a way of making the midpoint of the long edge of the document aim at the midpoint of the document fixer; moving the document fixer according to the size of the document to make the midpoint of the document fixer aim at a symbolic label on the laptop computer; and extracting the document image and processing the document image. In the method, the document is positioned by making the document fixer aim at the label on the laptop computer, so that the image which is clear and not skew can be obtained.