Abstract: To explore the influence of deoxidizing elements on the additive manufactured martensitic stainless steels, four types of martensitic stainless steel powders were prepared by different powder-making methods. The printed samples were carried out by selective laser melting under different process parameters, the effects of deoxidizing elements (Ti and La) and powder preparation process on the morphology and distribution of oxides, microstructure, and mechanical properties of the additive manufactured martensitic stainless steels were investigated. In the results, the deoxidizing element Ti can combine with Al₂O₃ to form Al‒Ti‒O composite inclusions, reducing the size of oxides in the samples, especially that of Al₂O₃. La has a stronger deoxidation capacity than Ti. The addition of La significantly reduces the quantity density and size of the large-sized oxide particles in the printed samples, and enhances the tensile strength and elongation of the printed samples contained La powders. Under a laser power of 150 W and 700 mm/s, the tensile strength and elongation of the printed samples by plasma spheroidized powders are significantly higher than those of the printed samples by gas atomized powders. The combined effects of the powder surface oxide layer, the powder sphericity, the oxygen content, and the deoxidizing elements change the mechanical properties of the printed samples. The variation trend of the depth-to-width ratio of the molten pool obtained by ChatGPT-4.0 is consistent with that obtained by the manual measurement, but there is a significant difference in numerical values, which indicates that ChatGPT-4.0 shows the certain reliability in materials science applications, but the accuracy still needs to be further improved.