The invention relates to acid solution used for processing the magnesium alloy surface. The acid solution is water solution which contains acids, inhibitor and wetting agent, wherein, the acids are first acids or mixture of first acids and second acids; the first acids are selected from one type or a plurality of types among citric acids, oxalic acids, tartaric acids, methanoic acids, acetic acids, metacetonic acids, butyric acids, glutaric acids, phenylformic acids, benzene dicarboxylic acids, lactic acids, glycolic acids, glyoxylic acids and amino acids; and the second acids are hydrochloric acids and/or nitric acids. By adoption of the acid solution, the magnesium alloy surface can be fully activated; the membranous layer of a converting film which is formed on the magnesium alloy surface after chemical conversion process is compact, has erosion resistance and good binding force with a paint film. Moreover, the method is a environment-friendly method for processing the magnesium alloy surface.