In order to evaluate the flood control and drainage capacities of different drainage schemes in the factory area of the offshore region, the MIKE21 model was used to simulate the overland flow drainage process in the factory area, and the MIKE11 model was coupled with the MIKE21 model to simulate the open channel drainage process in the factory area. The MIKE URBAN model was coupled with the MIKE21 model to simulate the pipeline drainage process in the factory area. The drainage processes in the factory area under the special combination scenarios of extreme rainstorms occurring inside the factory area, with the outside of the factory area encountering the backwater effect of floods were studied under the overland flow drainage, open channel drainage, and pipeline drainage schemes, and the water accumulation depth inside the factory area and the spatio-temporal changes of floods at different locations were obtained. The results show that under the overland flow drainage, open channel drainage, and pipeline drainage schemes, the maximum water accumulation depths in the factory area are 0.073, 0.125, and 0.087 m, respectively. The overland flow drainage scheme has the best effect, and the open channel drainage scheme has the worst effect; raising the height of the factory site can reduce the impact of the backwater effect of external floods during the flood peak period on the pipeline drainage and open channel drainage schemes.