A method and a system for measuring a distance from a reference point to an object are provided. The method comprises the following steps. At least one image of an object is captured through a lens comprising a phase mask composed of a parallel plate and a wedge prism. At least two corresponding regions of interest (ROI) are obtained from the images. The regions of interest correspond to identical portions of the object. The relative coordinates between corresponding locations within the corresponding regions of interest is measured. The distance is calculated according to the relative coordinates.