Abstract: The effects of NaCl and SO₂ on the initial atmospheric corrosion of AZ91D magnesium alloy were studied with a simulated atmospheric corrosion system. The analyses of surface morphology, corrosion products and rust layer structure were integrated by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) to investigate the corrosion performance. The results showed that NaCl accelerated the initial atmospheric corrosion of the alloy. The protective film was destroyed in the initial period, but the corrosion rate slowed down because of the formation of slight soluble corrosion products in the later periods in the presence of NaCl. Soluble corrosion products with no inhibitive function developed and partly solved to form the ions of free motion when NaCl and SO₂ existed simultaneously. A great deal of these products were very difficult to grow on the surface in a short time. The combined effect of NaCl and SO₂ on the initial atmospheric corrosion was greater than that caused by each single component.