Abstract: Copper-based niobium thin film cavity is one kind of superconducting radio frequency(SRF) cavities developed from bulk niobium cavity. This new type of cavity has similar SRF properties to the pure niobium cavities but is more economical, mechanically stable, and thermally stable, making it promising for industrial SRF applications. However, the inevitable surface defects of niobium film on the surface of Nb/Cu cavities induce extra power dissipation, and require post-treatment before cavity operation. Near-surface annealing of SRF cavity by nanosecond high-intensity pulsed laser is an emerging surface treatment technology for SRF cavity. Using high power and short pulsed laser with peak power flux exceeding 100 MW/cm² to locally recrystallize the surface can reduce the surface roughness, increase the grain size and eliminates some surface defects, so as to obtain better surface RF properties. At present, the type of laser selected in this direction is mainly the solid-state laser with high peak power, which has a very low average power, not practical for the actual superconducting cavity with an m² inner wall surface area. To solve this issue, a whole-cavity laser processing system based on a kW-level power nanosecond pulse fiber laser has been established by the Surface Treatment Research Team of the Institute of Modern Physics. In this study, finite element simulation was conducted with the parameters of the system to investigate the temperature distribution on the surface and inside the material under near-actual working conditions. Combined with the material properties, the laser surface treatment effect of pure niobium material was simulated. This study preliminarily confirms the feasibility of using nanosecond pulse laser for complete annealing of the inner wall of superconducting cavities, and provides an effective method for achieving better RF superconducting performance.