Flexible lifting undocking method for ultra-large catamaran semi-submersible platform

The invention discloses a flexible lifting undocking method for an ultra-large catamaran semi-submersible platform. The method adopts a lifting barge as a lifting device, the depth of water in a dockis increased or reduced by controlling a dock door sea valve, the lifting barge is pulled to the position below the catamaran semi-submersible platform, then the dock door sea valve is opened, so thatthe lifting barge is floated upwards along with rising of water surface, lifting force is provided for the catamaran semi-submersible platform, and the waterline of the catamaran semi-submersible platform during undocking is reduced. After the platform is carried out of a dock and moored alongside a deepwater wharf by the lifting barge, the lifting barge is ballasted to dive so as to be separatedfrom the catamaran semi-submersible platform. Therefore, the method solves the problem that the ultra-large catamaran semi-submersible platform cannot be undocked due to the fact that the waterline is too large is solved, not