Abstract: This study is an experiment of using digital seismic records to find the coda Q and its dependence on freqency. Data are recorded by triggered digital seismometers,and then are put into a microcomputer. After narrow band-pass filtering of the digital records,the digital seismograms become a set of pseudo-single frequency records. With the approach of time series analysis,decay curves of energy density against time are plotted. These curves are more reliable than those from visual seismograms. Fitting these decay curves to theoretical expression of a scattering model,the coda Q and its dependence on freqency are obtained. It can be noticed that these results are not constant for a certain station. The coda Q obtained is a function of time window which is the whole duration time of the coda used for study. The reason of this relation may be due to the difference in sampling area and depth for different arrival time of codas and the effect of multiple scattering. Therefore,when considering the coda Q as an earthquake prediction parameter,the duration time is an important factor to make choice.