Slab laser has characteristics of high output power and high beam quality. However, the far field facula of its primitive outgoing beam presents as an oval, and its far field divergence angle is slightly big which makes it inconvenient to transmit in very long distance. To solve this problem, a cylindrical telescope system with optimized parameter was used to expand the x-scale outgoing beam (wide divergence angle). The goal is to make the x-scale divergence angle approximate to the y-scale divergence angle which is a small angle, and constrain the beam waist position of x-scale and y-scale to the same place in case of out of focus. The general sphere beam expander was used to compress far field divergence angle of the reshaped beam. At last, the laser beam with a far field divergence angle less than 100 μrad and ratio of x-scale to y-scale less than 1.1 in out-field experiment was obtained.