Abstract: Vacuum diffusion Q235 steel after hop dip aluminizing was welded by tungsten gas arc welding. The effect of fusion welding on microstructure and high-temperature (800 ℃) oxidation resistance of the aluminized layer was investigated by means of optical microscopy, scanning electron microscopy, energy dispersive spectra and X-ray diffraction. The results show that the interface between aluminized layer and welding seam was metallurgical bonding. The elements of Cr, Ni and Al near fusion line gradiently distributed. The main phases near fusion line were Al2Cr, AlCrFe2 and (Fe, Cr) solid solution. The oxidation-mass gain curves of the post-weld sample were nearly parabolic. The main phases of the oxidation film in fusion zone were Al2O3, Cr2O3 and Fe2O3. Comparing with the high-temperature oxidation resistance of the aluminized sample before welding , the one of the sample after welding only decreased by 22.8%.