Developing a high-sulfur-tolerant catalyst is a practical concern for obtaining hydrogen through steam reforming of liquid hydrocarbon fuels. Ni-Pt/Al2O3 catalysts were prepared and applied in steam reforming of n-dodecane, a kind of model compound of jet fuel, containing sulfur. The Ni-Pt/Al2O3 catalyst gave a 14% deactivation degree under 50 ppm of thiophene in 10 h, which was less than that of Ni/Al2O3 with a 57% deactivation degree. At the same time, a H-2 molar yield after 10 h was as high as 3-fold in comparison to that of the Ni/Al2O3 catalyst. Characterization techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, H-2 temperature-programmed reduction, transmission electron microscopy, thermogravimetric analysis, and Raman spectra, were applied to explore the properties of these catalysts. Characterization results indicated the formation of the NiPt alloy for the Pt-modified catalysts, thus resulting in a small-particle and more moderate metal-support interaction of NiO species, which contributed to a high H-2 yield, thus leading to an improved sulfur tolerance. Much more graphitization carbon on Ni/Al2O3 under the presence of sulfur and the addition of Pt greatly reduced the carbon deposition through forming more easily gasified carbon, thus resulting in easy removal.