The work aims to seal the thermal spray coating with sealant, and study effect of sealing on the thermal corrosion resistance of the coating to improve the corrosion resistance of thermal spray coatings in severe environments in view of that the existence of pores and defects in thermal spray coatings is one of the important reasons for coating failure. Inconel 625 coating was prepared on 20# steel substrate by high velocity oxygen fuel spray deposition. The sealing agent was prepared with TEOS as the sealing agent base material and Cr2O3, Al2O3, ZrO2 and CeO2 as fillers. Then, the sealing agent was used to seal the pores existed in the Inconel625 coating. The effect of sealing agent on corrosion resistance of coating was studied and the coatings with and without sealing agent were corroded in film of mixed salts 75wt%Na2SO4+25wt%NaCl (mass fraction) at 650 ℃, and the change of sample mass was obtained at intervals during the test to study the corrosion kinetic. The compositions, structures and morphologies of corrosion products were investigated by XRD, SEM and EDS. For unsealed Inconel 625 coating, the gained mass was about 4.4 mg/cm2 after 160 h. The unsealed Inconel 625 coating had a duplex microstructure and the outer Ni-rich layer was looser and porous, and the inner Cr-rich layer was compact. Meanwhile, the S element was detected at the coating/corrosion interface. For sealed Inconel 625 coating, the mass loss was about 0.45 mg/cm2 after 160 h because the sealing agent dissolved in the molten salt during the corrosion process. During the corrosion process, Ni diffused in the sealing layer and oxidized to fill the defects of the sealed layer. A Cr2O3-rich oxide layer formed at the coating/sealed layer interface, and then further improved the hot corrosion resistance of the sealed coating. The sealant improves the compactness of the coating and effectively inhibits the diffusion of corrosive media in the thermal spray coating. Then, the hot corrosion resistance of Inconel 625 coating is improved obviously through sealing.