Abstract: A tank to simulate a fuel assembly's environment and mechanical boundary condition is designed.In aseismatic reactor core test,the nonlinear vibrational behavior of the fuel assembly is studied.The system which was installed in vibration table under 42 environments was excited by white noise,and a series of curves about relationship between fuel assembly's response and excitation under different direction,different medium,different excitation magnitude were obtained.As excitation magnitude increases,the 1st resonant frequency of the parallel plate fuel assembly decreases.Compared with that in air,the 1st resonant frequency of the parallel plate fuel assembly in water decreases greatly,and the nonlinear vibrational characteristic is soft spring.On the other hand,the damp of fuel assembly in water increases greatly and restrains the aseismatic response greatly.