Abstract: Based on ANSYS12.1, this paper studies the direct input method of a seismic acceleration. This method can avoid the numerical error produced by two times of numerical integral and also avoid the Rayleigh damping force produced by large mass method. Through the theoretical analysis and numerical calculation, the direct input method of a seismic acceleration is checked and compared with the direct displacement excitation method, the uniform acceleration excitation method and the large mass method. The results show that the direct input method of a seismic acceleration can be applied in practical engineering calculation.