Aiming at the de-ballast mode of the fast de-ballast system in semi-submersible lifting and disassembling platform, pressurized fast de-ballast method and balanced fast de-ballast method are proposed. The mathematical model of fast de-ballast system is established. A simulation model is established 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, flow rate and liquid level in the fast de-ballast tank based on two fast de-ballast modes are analyzed, and the advantages and disadvantages of the two fast de-ballast modes are compared. The results show that the balanced fast de-ballast method is safer than the pressurized fast de-ballast method with the similar time.