The invention discloses a discharge excitation gas laser and an operation method thereof. The laser comprises a laser main body, a discharge pumping source, a resonant cavity, a light window, a gas source, and an in-cavity pressure maintaining unit. The light window consists of a light window cleaner and a window. The light window cleaner is based on the gas turbulent flow energy dissipating principle, and comprises an energy dissipating box, a metal gas pipe, and a gas flow controller. When the discharge excitation gas laser operates, the gas source continuously provide laser working gas for the light window cleaner at a certain flow rate, and forms a turbulent flow in the laser light window, thereby reducing the kinetic energy of discharge particles in flying to the window, enabling the discharge particles not to reach and attach to the inner surface of window glass, and protecting the light window of the laser from being polluted. The inputted gas is discharged from the laser cavity through the in-cavity pressure maintaining unit, and the internal gas pressure of the laser cavity remains constant.