The work aims to optimize the preparation process of nanopore on stainless steel surface by the orthogonal ex-periment. The orthogonal experiment was designed by Taguchi experimental method to optimize the process. Nanopores were prepared by anodization of nitric acid solution containing sodium chloride and thiourea and expanded in aqueous solution con-taining sodium chloride, hydrochloric acid and sulfuric acid. The surface morphology and elements of the treated samples were analyzed by scanning electron microscopy & energy spectrometry. The porosity of the SEM images was counted by software. Porosity was used as a response indicator and the influence level and significance of the anodizing process and the expanding time on the surface morphology and porosity were studied by the range analysis and variable analysis and the process parameters were optimized. The SEM photograph and the mean value of the five levels indicated that the increase in nitric acid concentration was beneficial to increase the porosity and the higher thiourea concentration was favorable for the formation of a uniform ordered nanoporous structure. The sodium chloride concentration, oxidation time, oxidation voltage and expanding time had no significant effect on surface morphology and porosity. Elemental analysis indicated that the material of the nanopores was still stainless steel rather than metal oxide. The process parameters optimized by orthogonal experiment are: nitric acid concentration of 90 mL/L, thiourea concentration of 3.5 g/L, sodium chloride concentration of 20 g/L, oxidation time of 120 s, oxidation voltage of 5.0 V, and expanding time of 50 s. Through experimental verification, a nanoporous structure with flat surface and high porosity can be prepared by optimized process.