Semi-submersible support platform and positioning method thereof

A semi-submersible support platform, used for operations at sea after sailed to a certain position of a sea surface, comprising an upper deck and a lower pontoon, the upper deck and the lower pontoon being connected by a plurality of upright columns, each upright column being provided with a support leg that is longitudinally inserted through the upright column, the lower pontoon having a plurality of chambers therein, the chambers being configured to receive water therein so that the lower pontoon can sink downwardly when the water is introduced into the chambers or float upwardly when the water is drained out, the support leg having a compartment, the compartment being configured to receive water therein so that the support leg can sink downwardly when the water is introduced into the compartment or float upwardly when the water is drained out;

• each upright column including a leveling mechanism therein, wherein when the support leg sinks to reach the seabed, the leveling mechanism in each upright column is combined with the support leg to support the support leg, the leveling mechanism can drive the upper deck to move up or down along the support leg.