A method of Fourier transform dielectric spectrometer is described, it leads to simplifying the process of solving spectrum and to save the memory capacity for data. Using this method, it is shown that for the same dielectric sample the free and random relaxation will appear under different condition in the time range of 106 to 10-4 seconds, that was predicted by the phe-nomenoiogical theory. The relaxation times are related to the resistance R of the measurement circuit joinning the two electrodes of the sample.. Large value of R leads to a relaxation time of open circuit, and small ones lead to the limit of short circuit; the relaxation time of open ciecuit may be as large as 106 times of the short circuit one. The variation in frequancy domain spectrums of complex dielectric constant is given from open to short circuit cases.