1. A distance measurement method, comprising; projecting a light beam with a speckle pattern to a plurality of reference flat surfaces and an object which are located at different position points, so as to show an image of the speckle pattern on each of the plurality of reference flat surfaces and the object respectively, wherein the speckle pattern contains a plurality of speckles; obtaining a plurality of reference image information through capturing the image of the speckle pattern on each of the plurality of reference flat surfaces; obtaining an object image information through capturing the image of the speckle pattern on the object; obtaining a plurality of comparison results through comparing the plurality of reference image information with the object image information; and computing the position of the object through performing an interpolation operation to the plurality of comparison results; wherein the step of obtaining the plurality of comparison results through comparing the plurality of reference image information with the object image information comprises: obtaining a plurality of similarity scores through comparing the plurality of reference image information with the object image information, and defining the plurality of similarity scores as the plurality of comparison results; wherein the step of computing the position of the object through performing an interpolation operation to the plurality of comparison results comprises: selecting at least two similarity scores with highest values from the plurality of similarity scores; and computing the position of the object through performing the interpolation operation to a ratio of these at least two similarity scores with highest values.