One laser beamexpander is developed with clear aperture Φ=300mm and magnification β=30，Visual field 2ω=±1mrad.It works at three kinds of wavelength.The major wavelength is λ=0.6328nm,the others are λ=0.532μm,1.064μm.All the glass elements are made of Schott fused silica.The frontobjective focal length F=800 mm which is high order aspherical surface.After measurement with interferometer,the wavefront error of system peak to valley (PV) is better than λ/7,root mean square (RMS) is better than λ/50.