The in-depth study of infiltration process of simulated molten silicon in the porous preform of silicon carbide not only helps to understand the causes of defects in the reaction infiltration process, but also is of great significance to reveal the causes of special infiltration phenomena. In this paper, based on level set method, N-S equation and Young’s equation, the simulation of capillary infiltration process of molten silicon was carried out in the two-dimensional channel extracted and reconstructed by optical microscope image. The infiltration process of preform composed of 40 μm particles by molding and the preform based on particle gradation process was simulated. The results show that the larger inlet in infiltration process is conducive to rapid infiltration. The infiltration process gradually evolves from unsaturated infiltration to saturated infiltration in the same area. The pore structure of large cavity, sharp corner area and blind hole in preform will have a greater probability to evolve pore type defects. The boundary conditions of exhaust outlet of preform has a strong correlation with skin-forming phenomenon of infiltration.