In the design of CAP1400 Reactor Vessel Internals (RVI), because of systemic and non-linear properties, it is difficult to predict the flow induced vibration (FIV) load of Radical Support Key.The traditional way is to get the FIV load of Radical Support Key by over conservative methods, based on the linear PSD analysis for single component.A new simplified method to calculate the FIV load of CAP1400 Reactor Internals-Radial Support Key was proposed in this work, which considers the non-linear effects such as gap, stiffness, and friction, and thus gets more accurate results.A simplified beam model was developed for the CAP1400 lower internals, and has was verified by a CAP1400 RVI 1/6 scale model dynamic property test.The downcomer PSD load was transferred to time history load.The time-history analysis method was verified by scale model test results.The time-history downcomer turbulence load was then applied to the beam model to calculate the FIV load of CAP1400 Radial Support Key in various gap conditions.