For single laser cladding, the temperature field of the laser cladding was obtained by numerical simulation. Ni-based laser cladding layers were prepared on the surfaces of Q235 steel substrates by laser cladding experiments. Based on the theory of material phase transition, the formation mechanism of the microstructure at different depths of the cladding layer was analyzed, and the effect of adding CeO2 and TiO2 nanoparticles on the cladding structure was studied. The results show that in the process of laser cladding, under the combined actions of laser irradiation and heat conduction, the temperature variation characteristics of the cladding layer and matrix at different depths are different. This leads to different types of phase transitions, resulting in different microstructures. The addition of CeO2 and TiO2 nanoparticles to the cladding powder can change the chemical composition and microstructure of the cladding structure by influencing the phase transition process of the material,the nucleation rate is improved, and an uniform and fine cladding layer is obtained.