Shrinkage cavity may be detrimental to mechanical performances of casting parts. As a consequence,design engineers often use overly large safety factors in many designs due to insufficient understanding of quantitative effects of shrinkage cavity defects. In this paper, process of Al alloy wheel impact test was computationally analyzed for both the wheel models with and without shrinkage cavity defects. Based on shrinkage cavity data obtained from industrial CT(Computerized Tomography), the shrinkage cavity defects were modeled with SSM(Shape Simplification Method), which reconstructs shrinkage cavity defects to hollow spheroid primitives. After the impact simulation was conducted, the results show that under impact test condition, the wheel considering shrinkage cavity defects may fracture while the sound-assumed wheel may not.