To enhance the helicopter’s water surface buoyancy and reduce its dependence on emergency flotation bags, a reserve fuel tank solution based on the “dual resonance” principle of fuel tank and fuel motion was developed. Through altering variables including tank dimensions, total fuel capacity, and installation positions, 11 basic tank schemes were designed and analyzed for roll amplitude response operators. The data results indicated that among all parameters, the vertical position and cross-sectional area of the fuel tank are key factors affecting helicopter roll motion characteristics. The optimized tank scheme designed with these parameters can reduce the maximum amplitude response of the helicopter by approximately 12.3%. Particularly when encountering beam sea and large-angle head/following sea conditions, the roll response amplitude can be decreased by over 1.2°.