The galvanic corrosion of an AZ91D magnesium alloy coupled with 316L stainless steel using accelerated testing in salt spray fog has been investigated by using the scanning Kelvin probe (SKP) technique. The results show that the galvanic effects for AZ91D magnesium alloys are affected by the potential difference between anode and cathode by analyzing corrosion products and SKP Volta potential maps. The galvanic effect of AZ91D magnesium alloy coupled with 316L stainless steel is very significant during accelerated testing in the initial stage of salt spray fog because the potential difference between AZ91D magnesium alloy and 316L stainless steel is about –1.28 V. The galvanic corrosion occurs mainly in the interface near AZ91D magnesium alloy, and 316L stainless steel has no obvious corrosion. With the salt spray test time increasing, the corrosion of the AZ91D magnesium alloy is accelerated and the coverage area of corrosion products expanded. The Volta potential difference of galvanic sample increases from –1.29 V to –1.53 V after 24 h salt spray test. The galvanic corrosion effect of AZ91D magnesium alloy is increased. The corrosion products of AZ91D magnesium alloy have a protective effect. The galvanic corrosion effect is reduced when the corrosion product increases to cover the surface of the specimen