Intensive snowfall causes heavy snow load on the roof of buildings. Meanwhile, complex migration of snow particles would occur on surface of roof due to wind, which would cause heavier snow loading on roof than design specification. Changsha airport terminal 3 has a super-large structure with a very complex shape and large-span roof. In this paper, a numerical simulation was carried out on snow loading distribution of its roof and the design value was discussed. Migration of snow particles was simulated by means of Volume of Fluid (VOF) model and volume fractions of both air and snow phase were obtained. Numerical simulation results showed that snow migration has a significant effect on snow distribution of multi-level roofs, resulting in uneven snow load distribution. Moreover, snow load envelope was designed in accordance with the specification and the snow load distribution coefficients of lobby and corridor were obtained, applicable for further structural design.