Based on the actual welding process of rectifier sample structure, the numerical simulation of high temperature vacuum nickel-based alloy brazing process was carried out, and the flow model of melting-wetting filling weld of nickel-based alloy filler metal in high temperature brazing vacuum furnace was established. The numerical calculation was based on the volume of fluid(VOF) method. Considering the factors such as surface tension, gravity, and latent heat of phase change, the laminar flow model was used to solve the flow behavior of the solder with time. The distribution of solid and liquid solder and the distribution of temperature field were calculated. The phenomenon of braze material loss and weld bead formation on the surface of the base material, along with a good filling effect of the braze material inside the weld seam, verifies the rationality of the arrangement of solder and temperature control in this brazing process. An empirical formula for the volume ratio of braze material filling the weld seam with respect to time and temperature has been provided, offering guidance for actual brazing processes.