Abstract In this paper, an optical array resonator with phase-shifting end mirror has been combined with the RF-excited diffusively cooled slab waveguide CO2 lasers to obtain a desirable output laser beam with single-peaked far-field intensity distribution, which is highly spatially suppressed with the merits of high brightness and good characteristics of propagation. In the experiments, a maximum output power of 46 W and highest conversion efficiency of 11.3% have been obtained from a 200-mm-gain-length device. The laser beam intensity distribution acquired has similar characteristics to the ouptut beam from laser arrays due to the periodical structure of the phase-shifting total reflector, and has an excellent stability due to the mode-selection capability of this type of resonator. In this paper, theoretical analysis is also given, based on which corresponding theoretical model is established, the practical feasibility is shown, and the laser beam output with characteristics of in-phase array mode is predicted. The systematical experimental investigation indicates the prominent influence of the parameters of the phase-shifting array end mirror on the property of the output beam. Furthermore, the manufacturing errors of the phase-shifted array resonator are analyzed and the analysis provides a theoretical guide to the design of this type of lasers.