根据尾波观测的经验公式，选用了北京遥测台网昌黎台１９８９～１９９１年间所记录３３个ＭＬ为２．１～３．５地震的数字化资料，采用单台尾波解法，得到该台站所在地区的尾波Ｑ值和各地震的震源因子．进一步假设一定的震源模型，可得台站所在场地的频率响应和震源谱及其拐角频率、地震矩和应力降等震源参数；并试用于监测其在较大的地震前后的变化情况．由于尾波方法能较有效地消除震源辐射因子和单一路径的影响，故易于得到较多的信息和较高的精度，为研究震源的性质及探索震源参数在大地震前的变化提供了一个可能的方法 According to the empirical formula of coda wave observation, the digital data of 33 ML 2.1 ~ 3.5 earthquakes recorded by Changli station of Beijing telemetry network from 1989 to 1991 are selected. The single coda wave method is used to obtain the data of the stations Regional coda Q value and source factors of each earthquake. We further assume that a certain hypocenter model can be used to obtain the frequency response and the source spectrum of the station where the station is located, the source parameters such as the corner frequency, seismic moment and stress drop, and to test its changes before and after a large earthquake. Because the coda method can effectively eliminate the influence of source radiation factor and single path, it is easy to get more information and higher accuracy, which provides a possibility for studying the nature of the source and exploring the change of the source parameters before the major earthquake Methods