1. A distance measurement system, comprising: at least one reference plane; a light source module, providing a light beam having a speckle pattern to the at least one reference plane and an object, so as to show a plurality of images having the speckle pattern on the at least one reference plane and a surface of the object, wherein the speckle pattern has a plurality of speckles; an image capture device, capturing the image shown on the reference plane to generate a reference image information, and capturing the image shown on the surface of the object to generate an object image information; and a processing module, coupled to the image capture device for obtaining the reference image information and the object image information, calculating a plurality of brightness relationships between each of the speckles and adjacent speckles rounding each speckle in the reference image information and the object image information, and using a predetermined formula to calculate the brightness of each of the speckles and adjacent speckles rounding each speckle, in order to obtain a relative brightness information of each of the speckles, so as to calculate the distance between the distance measurement system and the object according to the relative brightness information; wherein the predetermined formula is a value, which is obtained by dividing the brightness of each speckle by a summation of the brightness of each speckle and the average of brightness of each speckle and adjacent speckles rounding each speckle.