The work aims to overcome the short comings of poor surface quality of aluminized layer and powder boning during aluminizing process and prepare an aluminized layer resistant to high temperature oxidation，high temperature sulfurization and corrosion on the surface of Q235 steel in an atmosphere not protected by inert gas. Aluminizing by powder pack cementation was adopt to change the filler constituent of aluminizing medium to solve the problem of poor surface quality caused by bonding of aluminizing medium. The effect of aluminizing temperature and holding time on the surface quality and thickness of aluminized layer was studied to determine the best aluminizing condition. The surface quality and the thickness of the aluminized layer were observed by electron microscope. The distributions of main elements on aluminized layer were analyzed by energy spectrometer. The phase composition of aluminized layer was studied by XRD. The hardness change in the aluminized layer was detected by microhardness tester. An aluminized layer with a thickness of about 370 μm was prepared by the powder composed of 15% aluminum powder, 5% ammonium chloride, 75% alumina and 5% graphite under 900 ℃ for 4 hours in a non-protective atmosphere. The aluminized layer was aluminide layer, transition layer and matrix from outside to inside. The aluminide layer mainly contained two elements including Al and Fe and the atomic ratio remained at 7:3. The main phase was Fe2Al5 and the hardness of aluminide layer reached 896HV0.1 which was much higher than that of the substrate. Adding some graphite in the powder can improve the surface quality of the aluminized layer and increase the thickness of the layer, while excessive graphite powder is not beneficial to the improvement of surface quality and the thickness growth of aluminized layer. The thickness of the aluminized layer increases first and then decreases with the increasing of the aluminizing temperature and has a parabolic relationship with the holding time.