Abstract: Cracks were often found in 20CrMnTi gear steel during processing. The cracking characteristics of 20CrMnTi gear steel caused by casting defects were analyzed by means of macro and micro examination. The results indicate that the cracks caused by subsurface bubble on the casting surface were smooth, the crack tail was obtuse, and severe oxidation decarburization phenomenon occurred at both sides of the cracks. At the cracking area caused by surface slag, crackle inclusions and carburet coexisted and grain at the cracking area had obvious directivity. More inclusions in the casting blank would result in tiny surface cracks defect on surface of the material during processing.