In order to study the microstructure evolution and mechanical properties of laser cladding coatings of high temperature alloy, a nickel-based NiCrFeMo high temperature alloy coating was prepared on the surface of 2Cr25Ni20 heat-resistant austenitic stainless steel using laser cladding technology. The cladding technology prepares a nickel-based NiCrFeMo high-temperature alloy coating on the surface of 2Cr25Ni20 heat-resistant austenitic stainless steel. Scanming electron microscope, X-ray diffraction, energy dispersive spectrometer, micro-hardness tester and other micro-analysis test methods were used to analyze the microstructure morphology, phase types, interface element distribution and segregation, and hardness of each area of the nickel-based superalloy coating. The results show that the bonding position of the base material and the cladding layer to the top of the cladding layer is sequentially generated from a variety of crystal grain morphologies. The Nb and Mo elements diffuse to the substrate under the action of the molten metal liquid convection, and the other elements basically have no diffusion. The cladding layer has phases: γ-Ni and Cr2Fe14C, while the bonding position of the cladding layer contains phases: Fe2Ni3, γ-(Fe, Ni), and Ni0.9Nb0.1. The average microhardness of the substrate is about 252HV0.3, and the average microhardness of the cladding layer is about 285HV0.3. In normal temperature tensile test, compared with the mechanical properties of 2Cr25Ni20 steel, the tensile strength of 2Cr25Ni20 steel repaired parts increases, the strength increases, the elongation after fracture decreases significantly, and the plasticity decreases. Therefore, this study provides a feasible plan for the subsequent repair of the steel furnace shaft.