Abstract:The current acceleration seismic design spectra has the disvatages including that its precision and the statistics features in different period stage have obvious differences, and the spectrum characteristics of the low-order spectrum based on the artificial signals mismatch the real statistics characteristics. The unified smooth spectrum which adopts unique function was presented based on the linear modle of displacement spectrum, and a new ground motion simulation method considering lower-order spectrum was proposed. The analysis results indicate that the smooth spectrum has the advantages such as simple form, high accuracy for all the period stages. The simulated earthquake signal fulfills the spectrum characteristic requirement for acceleration spectrum, velocity spectrum and displacement spectrum. The smooth spectrum has uniform characteristics including function form, the spectrum characteristics on multiple orders, elasto plasticity and multiple dimensions, and it is suitable for dynamic analysis and ground motion simulation.