In order to obtain the tri-dimensional seismic ground motion time histories which are compatible with the corresponding floor response spectra,the eigenfunctions of the sixth order ordinary differential equation are used as the basis functions to decompose and reconstruct the real recorded earthquake ground motion.By constructing the influence matrix,the amplitude coefficient of the eigenfunction is gradually adjusted through iterative calculation,and the preset fitting accuracy threshold is finally achieved.The orthogonalization procedure is introduced to ensure the statistical independence between the tri-directional time histories,and two sets of numerical examples are provided.The examples show that it is capable of achieving high matching accuracy between the response spectra of generated time histories and the target spectra.During the iteration,the time history response spectrum uniformly approaches the target spectra.The iterative process converges;the generated seismic time histories are drift-free and satisfy the code requirements.