Due to existence of chill microstructure and cracks, influence of flaw control with laser cladding NiCuFeBSi alloy and preheating are investigated. Mechanical property of alloy is estimated as well. Results show that chill microstructure width of NiCuFeBSi alloy is extremely low. With preheating temperature increasing, the chill microstructure become discontinuous. Because of the generation of chill microstructure in semi-molten zone, microhardness in this zone is highest while descending at two sides of interface. Tensile strength of alloy is higher than HT250, furthermore, tensile strength along cross direction is higher than longitudinal direction. However, tensile strength of butt samples is lowest because of heat affection. Failure type of claddings is mainly cleavage fracture mixing quasi-cleavage fracture.