Provided are a method and device for measuring a three-dimensional object in a non-contact manner. The method comprises following steps: providing a three-dimensional outline model of a three-dimensional object; establishing an image acquiring path according to the three-dimensional outline model; extracting a one-dimensional image and a two-dimensional image of the three-dimensional object with an image extracting unit according to an image acquiring path, drawing a two-dimensional outline model on the two-dimensional image or measuring the dimension of the two-dimensional image, wherein the two-dimensional outline model is established according to the image acquiring path and the three-dimensional outline model.