Abstract: By using finite element simulation software ProCAST, the formation of shrinkage porosity in the rejoined castings of Ni-based single crystal superalloy was investigated.The results show that the shrinkage porosity defects mainly appear in the last solidification zone of the rejoined platforms.Their formation are mainly affected by two factors.The one is the geometric structure of the casting, and the narrow rejoined platforms are not conducive to the liquid metal feeding.The early solidification metal will block the feeding channel of the subsequent solidification alloy at the platform.The other factor is the withdrawal rate.With the withdrawal rates increasing, the concave degree of solidification interface increases, the feeding is more difficult, and the formation range and number of shrinkage porosity increase simultaneously.