Improving the survivability of floating structures in harsh marine environments is the key to the large-scale engineering application of floating structures. The authors and their research team have innovatively proposed a new submersible floating mooring system to deal with extreme sea conditions. Being able to switch between floating and diving states according to the environmental conditions, the survivability and safety of floating structures can be guaranteed. Take a cellular modular floating structure as an example, the effectiveness of the proposed submersible floating mooring system was verified in this paper, by conducting the motion response analysis and mooring time domain analysis based on the ocean engineering software SESAM. The results show that the motion response and mooring line tension of the floating structure decrease with the increase of the diving depth. The vertical acceleration of the floating structure was reduced and the comfort was improved correspondingly through diving. The proposed submersible floating mooring system provides promising insights for the application of marine floating structures in extreme sea conditions.