Using geometrical optics, a laser beam homogenizer for high power CO2 has been designed. Laser beam is homogenized by means of waveguide, separate beam with spectroscope, so the device can be used to sintering ceramics on double sides. The waveguide is composed of a square-section tube with four flat rectangular mirrors, and its length is 200 mm, cross section 10 mm×10 mm. Two mirrors that has an angle with each other forms the spectroscope. The uniformity of the power distribution is stable without being affected by original laser beam. Using Fourier optics to analyze system, the method to improving the uniformity has been discussed. Because all the elements have reflecting surface, energy loss is not serious, optical path adjusting is convenient.