Abstract: In order to eliminate the impact of Pile-up phenomenon on the hardness of thick aluminum film of echelle grating in nano-indentation test, and obtain the accurate hardness value of aluminum film of echelle grating, a new hardness calculation method by modifying the contact projection area in O&P method was proposed.First of all, according to the groove depth of the echelle grating and adopting the CSM(continuous stiffness measurement), the nanoindentation hardness of the thick aluminum film of echelle grating with a pressing depth of 5 μm was tested.Secondly, SEM and AFM tests were carried out on the indentation position, and the results showed that pile-up phenomenon appeared in the nanoindentation hardness test of thick aluminum film.Finally, the analysis and extraction of nanoindentation data of aluminum film, and the recovery of indentation uplift morphology, etc. prove that the projected area edge of contact surface is a parabola, and then modify the calculation method of the projected area in O&P method.The results show that the hardness value of the thick aluminum film of the medium step grating increases with the increase of the pressing depth by the nano-indentation hardness test method, and the hardness value obtained by the modified contact projection area hardness correction method is about 40% lower than that obtained by the traditional O&P method