Torrential rainfalls have been observed frequently in recent years and these rainfalls caused inundations in urban and rural areas. Intensity of such rainfalls were sometimes excess over the design rainfall of drainage systems and rain was running over the road. In these floods, some portion of rainwater intruded into underground spaces and the users faced the danger of underground flooding. In this paper, underground flooding in a mega-underground mall were investigated by using 2D shallow flow model with structural mesh and evacuation from there was also studied with the criteria of safety evacuation obtained by evacuation tests. The results show that flooding processes and safety of evacuation are quite different in the two cases with and without the consideration of drainage system. It means that the inflow conditions into underground space are depend on calculation results of rainwater flooding.
