The invention relates to a carbon film for improving the abrasion resistance of magnesium alloy and a preparation method thereof. The carbon film is made of a diamond-like carbon film which contains metal elements with atom percentage of 2-10 percent. Compared with the prior art, the carbon film and the method have the advantages that: trace metal elements are introduced in the diamond-like carbon film, so that while the internal stress of the film is greatly reduced, the diamond-like carbon film has smaller hardness damage, the adhesive force of the diamond-like carbon film and the magnesium alloy base, and the service life of abrasion resistance of the magnesium alloy can be greatly improved.