This paper discusses the design the crystal structure, pump cavity, and laser resonator of high average power solid-state slab geometry laser. A laser with a output power of 1028 W at 100 Hz, and with a beam quality of M2x=—2.386 and M2y=2.528 has been developed. The instability of output power is less than 2.1% with in 0.5 h, and a pulse width is 0.238 ms.