The invention relates to the technical field of model ship tests in the field of ships and ocean engineering, in particular to a supporting device for a large opening model test of a sea-water directvessel. The supporting device comprises a retractable activating supporting mechanism and a fixed activating supporting mechanism. The retractable activating supporting mechanism is fixedly connectedwith the fixed activating supporting mechanism through a connecting plate. The retractable activating supporting mechanism includes a first hull supporting plate, an activating joint, an activating ball sleeve supporting base and a hydraulic jack. The top of activating joint is connected with the hull supporting plate. The bottom of the activating joint is connected with the activating ball sleevesupporting base. The bottom of the activating ball sleeve supporting base is connected with the hydraulic jack. The fixed activating supporting mechanism includes a second hull supporting plate, a fixed activating ball and a steel cushion block. The top of the fixed activating ball is connected with the second hull supporting plate. The bottom of the fixed activating ball is fixed on the top of the steel cushion block. The testing process and the actual situation are more appropriate, and the test result is more convincing.