A waveform inversion algorithm, based on least square method, has been applied to the P and S waves of the 26 December 2003 Bam earthquake. The aftershocks of this event distributed along a narrow zone (approximately 20km) in N-S direction. In this research, estimates of centroid depth, seismic moment, and source mechanism have been obtained. The source mechanism derived from the inversion of long period body waves revealed that two events occurred on N-S trending strike-slip fault with a thrust component. According to the source model estimated in this study, the Bam earthquake was a multiple event. The rupture following the first event started at a depth of about 8km. However depth of the second event is about 10km. The total seismic moment estimated from inversion processes is 8.34×1018Nm. The seismic moment of the second event is less than the first one (the seismic moment of second event is calculated as 2.34×1017Nm). The pulse duration of main shock and the second event was determined from source time function and it is 1.7s and 0.8s respectively. Corner frequency and source radius have been calculated for main shock and the second event by using pulse duration. The range of corner frequency and source radius are from 0.187Hz -0.397Hz and 5.47km-2.57km for main shock and second event, respectively.