Abstract: This paper investigated the cracking behavior of K418 superalloy block specimens during laser repair remanufacturing. It deeply analyzed the crack initiation mechanism and propagation patterns of K418 superalloy in this process, and focused on exploring the specific effects of substrate preheating treatment on its cracking characteristics and mechanical properties. Two primary types of cracks formed during laser repair are revealed: solidification cracks generated on the surface of already solidified regions during deposition, and liquefaction cracks originating from the heat-affected zone and extending into the repair area. The repair zone exhibits columnar crystal structures with epitaxial growth characteristics at the base, fine dendritic structures in the middle, while epitaxial dendritic growth is interrupted and oriented changes occur at the top. After preheating the substrate at 400 ℃, the repair zone shows significant dendritic coarsening. Microhardness measurements indicate that the repair zone's base has slightly higher hardness than the unpreheated sample, with minimal difference at the top, reaching a peak of 514 HV. Residual stress in the repair zone decreases dramatically to an average of 38 MPa. The ultimate tensile strength of preheated samples increases from 1125 MPa to 1234 MPa, while the elongation decreases from 10.5% to 8.1%, and its fracture mode is a mixed fracture pattern dominated by ductile fracture.