Abstract: The source parameters of the M=7.4 Bohai earthquake of July 18, 1969 and the M = 7.1 Yongshan, Yunnan earthquake of May 11, 1974 were studied with synthetic seismograms of long-period body waves. Full-wave theory seismograms with WKBJ approximation and real integral paths of teleseismic P + pP + sP phases at 20 WWS-SN stations for the Bohai earthquake and 7 WWSSN stations for the Yongshan earthquake were calculated. The synthetic seismograms were matched with the observed traces by trail-and-error to obtain the source parameters. The results are: For the Bohai earthquake, h = 25km, = 205, = 85, = -145, M0 = 2.4 1019N m, R = 25, L = 36km, VR = 6 km/s. For the Yongshan earthquake, two simultaneous sub-ruptures of h=15km were concerned and = 45, = 65, = 0, M0 = 1.9 1019N m, R = 225, L = 10km, VR = 1 km/s for the first one; and = 220, = 75, = 170, M0 = 1.3 1019N m, R = 30, L = 23km, vR=2 km/s for the second one, where is strike, dip, rake, M0 seismic moment, h depth, R fracture direction, L fracture length, and VR rupture speed.