Abstract: The problem of accurately measure the spectral characteristics of a seismic observational system is an important subject of investigation in seismology. At present, the usual method to measure and calculate is by separate sections. In this way, it requires not only a certain amount of instrumental work, but also neglects the mutual effect between the seismograph and the amplifier at their junction. As a result, neither can the phase-characteristics be directly determined by experiment nor accurate amplitude-frequency characteristics be obtained.In this paper, a method has been proposed for the determination of the spectral characteristics of any seismic observational system by means of Fourier Transform. It is called the TS-method. Two testing signals are used, a triangular and a step function pulse. If the dynamic response of the testing signals are known the spectral characteristics of the system under investigation can be found immediately.