Abstract: The collision of assemblies caused by flowinduced vibration and the fatigue damage caused by continuous fluid erosion threaten the safety of the reactor core. Therefore, it is necessary to study and evaluate the flow-induced vibration behavior of fast reactor assemblies. The uncertainty of vibration characteristics of assembly can be brought by either method with or without fixed convex platform constraint. In order to study the influence of convex platform constraints on the flow-induced vibration characteristics of fast reactor assembly, and quantitatively evaluate the influence of the presence or absence of convex platform constraints on component uncertainty, the flow-induced vibration characteristics of the assembly under two constraints, free upper end of the assembly and fixed convex platform constrains with 0.3 mm gap, were studied by experimental method in this paper. The experimental results show that the assembly has a relative deviation of 6.1% in maximum amplitude RMS with or without a fixed convex platform constraint, for the amplitude of the measuring point closest to the convex platform constraint, the relative deviation of the maximum amplitude RMS with or without boss constraint is 17.4%. The experimental result has some reference value for the analysis and evaluation of the flow-induced vibration behavior of assembly under such complex support conditions.