The effects of different heat input and multi-layer thermal cycle on the crack morphology, distribution, expansion mode and microstructure and hardness of the deposition zone were analyzed by laser deposition of DZ125 single-layer multilayer experiments. The results show that as the heat input increases, the number of low-melting eutectic increases, and the formed liquefaction cracks expand along the crystal and increase in size. Optimizing the process parameters and reducing the heat input can prevent from producing the cracks; as the number of sedimentary layers increases, the heat accumulation increases, the cooling rate decreases, the thermal stress increases, and the solidification crack expands in both the horizontal and longitudinal direction. The interlayer heat is reduced by interlayer cooling to obtain a single-channel multilayer crack-free structure. In the first layer of the deposition zone, the carbides gradually become round and the number decreases, and the hardness of the first layer decreases slowly.