Abstract: Nickel-base alloy Inconel718 was treated by QPQ.The film growth rate appears to be controlled by diffusion.And the case depth is in direct proportion to the square root of nitriding time.The temperature has great influence upon the depth of nitrided layer.The maximum hardness obtained by QPQ is about 3 times harder than that of core hardness.The nitrogen is found to react with Cr to form CrN, which is detected in the nitrided layer by X-ray diffraction analysis.Exterior film structure varies from columnar, which is observed using scanning electron microscopy(SEM).The distribution of nitrogen within the film is uniform and there is a sharp boundary between the film and substrate.