The water load static test of the amphibious aircraft is mainly to assess the structural strength of the aircraft under water surface landing conditions, including typical water landing conditions such as pontoon landing, bow landing and stern landing. Due to the unique structure of amphibious aircraft and the complexity of load, that is, the pontoon, the bow and the stern are similar to the cantilever beam structure, and the water load is the large load of threedimensional concentrated pressure,resulting in the deformation of the assessment area is much larger than that of the land aircraft.This large deformation causes the loading error in the vertical direction of the test site up to more than 10%.Aimed at the above problems, the load optimization and balancing technology based on structural deformation constraint was proposed,and the equilibrium load calculation model was established with the deflection as the optimization objective.By introducing the equilibrium equations of the total force and the total moment of the whole machine,the rigid body displacement in the water load assessment area was limited through the optimization of the test balancing load in the non-test site. The feasibility of the load balancing technology was verified by finite element analysis and test. The results show that the loading error in the vertical direction of the test site can be controlled within 1% by using the load optimization and balancing technique.