n-Decane steam reforming towards hydrogen has been researched in a fixed-bed reactor containing spherical particle of Ni supported La-Al2O3 catalyst. The as-prepared Ni/La-Al2O3 catalyst was modified by the alkaline promoters M(Na, K) in order to inhibit carbon deposition. The physicochemical properties of these catalysts were characterized by Nitrogen physisorption, X-ray diffraction, X-ray photoelectron spectroscopy, Infrared spectroscopy, Temperature programmed reduction/desorption, Scanning electron microscopy-energy dispersive X-ray spectroscopy. The results showed that the addition of alkaline modifiers had a slightly impact on the surface area, crystallinity and morphology of Ni/La-Al2O3 catalyst, but improved the activity and stability, as well as reduced the rate of carbon deposition formation and thereby increased the working life of the catalysts. Meaningfully, K was shown an excellent catalytic performance in inhibiting carbon deposition, and the presence of K-modifier prevented metal sintering and controlled Ni particle size and dispersion, strengthened the metal-support interaction, and decreased the acidity of catalysts.