The rectangular slabs discharge CO 2 laser array is described and the resonator parameters are given. The far field properties of the multi-beams exported from the laser array are studied quantitatively based on the Collins formula and the coordinate transformations. The numerical calculations indicate that the beams will superpose when the distance is very small (about several mm) between each other. The main parameters which influence the beam combination are given. Three methods are used for evaluating the beam quality of the output beam, such as, combination efficiency (CE), M 2 factor and power in the bucket (PIB). It is shown that the research results are valuable for the laser industrial processing.