Abstract: regarding the failure of the thin-walled sealing track made of 42CrMo steel in the main drive of shield machines due to wear during service, the commonly used laser cladding repair method is prone to causing workpiece deformation and interfacial cracks in the clad layer, resulting in high repair difficulty and a complex process flow. This paper proposes a novel repair process based on cold laser cladding technology. Without heat treatment or auxiliary transition cladding layers, an iron-based wear-resistant repair layer is directly deposited onto the surface of the high-hardness quenched layer of 42CrMo base material. Prepare substrate-functional layer process specimens to analyze the functional layer's properties, microstructure, and elemental distribution, thereby revealing the forming mechanism of crack-free cladding layers. Laser cladding was performed directly on a 42CrMo thin-walled annular ring (initial temperature 0-20°C), with crack propagation analyzed using penetrant testing. The results indicate that using the new process, a strong metallurgical bond can be formed between the functional layer and the base material. During cladding, the interlayer temperature is maintained at a low level, preventing deformation of thin-walled components due to heat accumulation. Microstructural analysis reveals that extremely rapid cooling rates combined with the low-temperature environment of the substrate promote the spontaneous formation of a bonding transition zone between the clad layer and the interface region. This significantly reduces residual stresses, achieving a breakthrough in crack resistance without requiring a transition layer or preheating/post-heating conditions. This research provides the theoretical basis and technical support for the efficient repair and remanufacturing of large-scale, high-carbon thin-walled structural steel components.