The typical defects resulting in the broken wire during the preparation of NbTi superconducting alloy wires was described. The formation mechanism of forging streamline, the Ti-riched segregation resulted from solute redistribution and the mechanism of streamline and black spots were analyzed. The results indicate that the Ti-riched segregation of NbTi alloy could be described by black spots and tree ring in X-ray photograph and the essence of this segregation is channel segregation. It is aimed to provide a method to optimize the preparation technology, which can eliminate the Ti-rich segregation and improve the constituent and microstructure homogeneity of NbTi superconducting alloy.