It is of great significance for the application of Ni-based single crystal superalloy in inhibiting the solidification crack and repairing the blade. The mechanism is to avoid the microstrucure transformed from columnar to equiaxed dendrites (CET), and to avoid the formation of dendritesin remelting zone. In this study, the relationship between crack sensitivity and grain size of DD6 alloy was investigated by laser cladding technology. The epitaxial growth of GH768 alloy deposited on DD6 single crystal superalloy was studied. The mechanism of laser processing parameters on the formation of single crystal structure was clarified. The results showed that with the increased of laser scanning speed, the grain size decreased, the regularity increased, and the solidification crack weakened. When the laser power was 250 W, the scanning speed was 2.5 mm/s, the lifting height was single layer was 100 μm, and the superposition rate was 41%, the solidification cracks could be eliminated and the damaged single crystal blade could be initially repaired.