CW-CO2 laser nitriding technique was applied to improve the properties (such as aging property and the core loss) of grain oriented silicon steel. The samples were nitrided with regular space. Laser power density and scanning speed were chosen as 7.8×105W·cm-2 and 100mm·min-1. By some laser irradiation, Fe4N and Fe3N were formed in the nitrided zone. The nitrided samples were annealed at the temperatures ranged from 100 to 900°C. The core loss of some interested samples was tested. The results show that the core loss of the nitrided samples with different thickness of 0.23 and 0.30mm decreased by 14.9% and 9.4% respectively, and the aging property were improved up to 800°C. The mechanism of laser nitriding to improve the properties of grain oriented silicon steel is discussed. CW-CO2 laser nitriding technique was applied to improve the properties (such as aging property and the core loss) of grain oriented silicon steel. The samples were nitrided with regular space. Laser power density and scanning speed were chosen as 7.8 × 10 5 W · cm -2 and 100 mm · min -1. By some laser irradiation, Fe 4 N and Fe 3 N were formed in the nitrided zone. The nitrided samples were annealed at the temperatures ranged from 100 to 900 ° C. The core loss of some interested samples was tested. The results show that the core loss of the nitrided samples with different thickness of 0.23 and 0.30 mm decreased by 14.9% and 9.4% respectively, and the aging property were improved up to 800 ° C. The mechanism of laser nitriding to improve the properties of grain oriented silicon steel is discussed.