1. A system for focusing discrete points on an under-measured object, the system comprising a computer and a measuring machine, wherein: the measuring machine is installed with a lens, a charge coupled device (CCD), and a laser aid, and the measuring machine is configured for obtaining an image of the under-measured object; and the computer comprises: an image acquiring card connected to the CCD through a cable, and configured for acquiring the image of the under-measured object from the CCD; and a focusing program, which comprises: a selecting module configured for selecting one or more measurement points on the image, and obtaining X-coordinate values and Y-coordinate values of the measurement points; a controlling module configured for controlling the laser aid to search solid points on the under-measured object by moving the measuring machine according to the X-coordinate values and the Y-coordinate values of the measurement points, to emit laser lights to the solid points, and to compute a vertical distance “h” between the laser aid and each of the solid points according to the laser light reflected from each solid point, wherein each solid point on the under-measured object corresponds to a specific measurement point on the image; a computing module configured for computing a Z-coordinate value of each of the measurement points according to the vertical distance “h”; and a focusing module configured for controlling the lens to focus the solid points one by one on the under-measured object by moving the measuring machine according to the X-coordinate value, the Y-coordinate value, and the Z-coordinate value of each measurement point.