Abstract: The application of the system nonlinearity detection based on Hilbert transform in earthquake engineering is studied.The basic principle of the system nonlinearity detection based on Hilbert transform and the relative quantitative index of the nonlinearity are introduced.Considering the influence of both input and output noises,a single-degree-of-freedom nonlinear structure was analyzed using numerical methods.Results show that with the increase in the peak earthquake acceleration,the difference between the amplitudes of the structure frequency response function and its Hilbert transform increases,and the relative quantitative index of the nonlinearity in the structure also increases.Hilbert transform and the relative quantitative index can detect the nonlinearity in structures and has certain theoretical value in structural control and health monitoring.