A distance measurement method comprising: projecting a light beam having a speckle pattern to at least one reference plane to show a plurality of images with the speckle pattern on the at least one reference plane. The speckle pattern has a plurality of speckles, so as to capture the image with the speckle pattern on the reference plane to obtain a plurality of reference image information. When the object enters the area illuminated by a light source module, an image with the speckle pattern on a surface of an object is captured to obtain an object image information. Then, a plurality of brightness relationships among each of the speckles with adjacent speckles rounding each speckle are computed according to the reference image and the object image information to obtain relative brightness information of each speckle, which is used to compute position of the object.