| The most stable adsorption position, geometry structure and gradual dehydrogenation NHx(x=1~3) on Ir (100), Ir (111) and Ir (110) surfaces have been investigated using density functional theory in slab model. The corresponding adsorption energy and activation energy were calculated. The results show that NH3 is found to be perpendicular to top position as C3 axis on Ir (100), Ir (111) surfaces, on Ir (110) , NH3 prefers the top site with inclining 68.6 of N-Ir bond relative to the surface, and the difference of adsorption energy depends on the diversity of the surface structure, NH3 is found to be more easily absorbed on open surfaces of Ir (100), Ir (110) . NH2 adsorbed on bridge site on three surfaces, on Ir (100), (111) surfaces NH favor hollow location, NH prefers short bridge site on Ir (110) surface, the adsorption energy decreased with the H atoms increasing .To the decomposition of NHx, on Ir(100), the adsorption and decomposition of NH3 is competitive, on Ir (110) NH3 dehydrogenation is easy to occur, NH3 is molecular adsorption on Ir (111), not decomposition. NH2, NH on the three surfaces can be decomposed, on Ir (110), the activation energies of H depletion for NH2, NH are higher. The above consequences could adequately indicate that the adsorption and dehydrogenation of NHx on Ir surfaces is structure sensitive.