Abstract: In order to study the focusing properties of Gaussian beams passing through a compound optical system consisting of two thin piano-convex lens,the formulae of the waist radius and imaging distance of focused Gaussian beams were deduced based on the matrix optical method.Then effect of various parameters in the optical system on its stability property and the waist radius was simulated by means of numerical calculation.Finally,the focusing properties of Gaussian beams passing through the compound optical system was discussed.The results showed that the system was capable of achieving both stability and smaller focused waist radius.The focus radius of about 2μm was achieved in the experiments,which proved the correctness of the theoretical analysis.The study built a foundation for the design of a solid state laser.