Abstract: There are defects in the casting process of automobile shell castings, which leads to high scrap rate. The casting defects were sampled and analyzed by SEM. It is found that the defects in casting are mainly sand inclusions, oxidized slag and composite defects of sand inclusions + oxidized slag. The defects are related to the setting of gating system, unclean removal of free sand in cavity, low strength of sand mold and incomplete removal of slag in molten steel. After adopting the measures of optimizing gating system, thoroughly removing the free sand particles in the mold cavity, increasing the strength of sand mold, setting ceramic filter in the gating system, the incidence of such casting defects is controlled below 3%.