A scanning device and a method thereof are provided. The scanning device includes a scanning platform and an optical chassis. The scanning platform is for supporting an object. A reference origin is defined on the scanning platform for positioning the object. The optical chassis is located at a detection position while detecting a position of the object. The optical chassis includes a carriage, an image sensor and a detector set. The image sensor is disposed in the carriage for capturing an image of the object and generating image data of the object. The detector set is mounted on the carriage for detecting whether the presence of the object is located at the reference origin.