Abstract: A new optical design of laser beam expander is introduced. It suits for three laser beams to be expanded and focused. Its operation wavelength is 1 080 nm and its full field of view 0.6 degrees. A two-mirror catoptrical telescope is designed for expanding and focusing three beams which are arranged in a close configuration. Its primary is an ellipsoid mirror with aperture diameter of 303 mm. Its focusing performance approaches to the diffraction limitation. And focusing at different target ranges is implemented through control of the axial position of the secondary mirror. The power density distribution and power in the bucket curve of combined and focused laser spots are calculated with the aid of computer simulation. When focused at one kilometer, the ratio of the spot power in the bucket of 9 mm radius to the total power is over 95 percent. This new kind beam expander has the advantages of simple and low length-to-aperture-diameter ratio. The system focusing performance satisfied the usage requirement. The power of laser spots is effectively combined.