Abstract: Least squares method is used to invert source parameters from data recorded by a three-component digital seismograph. It is found that the focal mechanism parameters of the September 1981 Luanxian,Hebei,earthquake swarms are: strike 98,dip 54,rake-114; that of the July 1982 Jianchuan,Yunnan,earthquake are: strike 199,dip 40,rake -110; that of the October 1982 Lulong,Hebei,earthquake are: first group,strike 270,dip 65,rake -135; second group,strike 195,dip 80,rake -165