Abstract: Due to its simple structural pattern and high cost-effectiveness, the gravity deep-water net cage has been always considered as the crucial facility to develop the deep-sea mariculture. However, the harsh marine environment in the deep sea poses a significant threat to the safety of cage facilities. Especially in the South China Sea, typhoon weather occurs from time to time. To ensure the profitability of deep-sea aquaculture, the development of safe and reliable net cage has become a consensus in the mariculture industry. Taking into account the deficiencies of traditional gravity-type deep-water net cages, this study presented a gravity-type liftable net cage. The core function of this liftable net cage is that it can submerge its main body into the sea before the typhoon arrives to avoid the impact of extreme sea conditions and ensure the safety of the cage facilities and farmed fish. To achieve the function, the steel truss structure was used to replace the HDPE floating collars in traditional cage and the steel ballast pontoons were arranged to connect the truss structure. Thus, it can control the ballast water to control the cage lifting. The change of ballast water was achieved by controlling the inflation and deflation pipelines connected to the pontoons. When the gas in the pontoons was released, the seawater would be injected into the pontoons to decrease its buoyancy and achieve the cage diving. Conversely, when the pontoons were inflated, the seawater would be released to increase the pontoon's buoyancy and achieve the cage rising. In addition, the integrated grid-type mooring system was used to replace the distributed mooring system in traditional cage. To evaluate the hydrodynamic properties of the liftable net cage, the physical model test of the cage in both floating and submerged states was conducted. During the test, the scale ratio of net cage's main body was 1:30. The variable scale similarity criterion was used to simulate the net system and the net with real scale net twine was selected in the test. Considering the different wave conditions, the comparative analyses of the cage with floating and submerged states were done from the perspectives of motion response and mooring force. The test results showed that the total average mooring force reduction of the cage under submerged state was more than 20% by comparing with the cage under normal floating state, and the maximum reduction was approximately 63.22%. Moreover, the maximum reduction of the wave side mooring force reached 66.54%, the maximum reduction of the front side mooring force reached 60.55%, the maximum reduction of the rear side mooring force reached 64.97% and the maximum reduction of the back wave side mooring force reached 58.39%. The results above can prove that the liftable net cage can successfully lower the chance of mooring lines breaking and enhance its mooring safety by diving itself into the water. Additionally, the average heave motion amplitude response of the cage under submerged state decreased by more than 20% by comparing with the cage under normal floating state, and the maximum decrease was about 48.50%. In terms of pitch motion amplitude, the maximum decrease of the cage was 58.41%. According to the results above, it was demonstrated that the liftable cage can effectively improve the structural safety and stability by diving itself into water. Besides, this work also has advised that the cage connecting ropes must focus on strengthening design in order to control the stability of the cage, because it was found that the surge motion amplitude of the cage under submerged state was much larger than the cage under floating condition. To sum up, this study has confirmed that the gravity-type liftable cage presented in this work can be used in extreme sea conditions. It can offer a new facility option for the growth of deep-sea aquaculture and provide necessary technical data to support this gravity-type liftable cage's further optimization.