In view of the de-ballast work demand of semi-submersible lifting and disassembling platform, a combined de-ballast mode of water pump and air compressor is proposed. The mathematical model of the de-ballast system is established, a simulation model is built in SimuWorks environment, and the typical operation condition is simulated such as lifting condition of 0-4 200 t by double cranes. The changes of air pressure, liquid level and seawater flow in the column ballast tank under the combined de-ballast are analyzed. The advantages and disadvantages of three methods, including air compressor fast de-ballast, water pump de-ballast and combined de-ballast, are compared. The simulation results show that the strategy of combined de-ballast can balance the stability, safety and rapidity of the semi-submersible lifting and disassembling platform in a better way.