Catalytic oxidation of nitrogen oxides is an important development direction of flue gas denitration technology. In this work, manganese-based NO oxidation catalysts were prepared by sol-gel method using the high alumina fly ash with spherical hollow structure as the carrier, and manganese nitrate as the source of the active component. Scanning electron microscopy (SEM), X-ray diffractometer (XRD), N2 physical adsorption, H2 programmed temperature analyzer (H2-TPR), and X-ray photoelectron spectroscopy (XPS) were used to analyze the catalyst performance and NO catalytic oxidation mechanism. The results showed that the particle size of the carrier, manganese loading, calcination temperature of manganese nitrate gel, and the catalytic oxidation temperature of NO had a great influence on the catalytic activity of the catalyst. The optimum temperature for calcining manganese nitrate gel was determined to be 500℃. The best catalytic oxidation effect with an oxidation rate of 77.8% at the NO catalytic oxidation reaction temperature of 290℃ was obtained when the particle size of the carrier is between 100~200 mesh and the manganese mass loading was 8wt%. SEM results showed that the manganese oxide particle diameters prepared by the sol-gel method were between 100~200 nm and relatively uniformly loaded on the carrier. N2 physical adsorption showed that the pore structures of the catalyst were mainly mesoporous and exhibit an H3 hysteresis loop. Chemisorption of oxygen Oβ proportion on manganese-based catalysts and Mn4+ concentration firstly increased with the increase of manganese loading and then decreased. This was consistent with the trend of catalytic oxidation performance, indicating that Oβ and Mn4+ are the decisive factors affecting the catalytic oxidation of NO.