An unstable resonator with seven large aperture ceramic disks and intra-cavity adaptive correction is presented. The composite ceramic disks with absorption rings were adopted to suppress amplified spontaneous emission. An intra-cavity aberration non-conjugate correction based on round-trip wavefront and relaxation iteration was applied in the resonator. After tilt and defocus were corrected in turn, an average output power of 4.5 kW was obtained. The corresponding beam quality factor β was 19.5. After tilt, defocus, and high order aberrations were corrected, the average output power was increased to 5.4 kW, and the beam quality factor β was improved to 6.8.