Abstract:In solving nonlinear inversion problem of two-dimensional SH-wave equation with the use of least square method,a Jeneral inversion problem of two-dimensional SH-wave equation can be reduced to a physically realizable optimal control problem in model space by introducing the nonlinear’functional of SH-wave velocity variation, so that synthetic seismogram of theoretical model is optimally fitted into real seismic record in the sense of least square. The optimal solotion is obtained by adopting gradient method,The gradient is calcufated from the forvrard wave field generated by real seismic sources and the backward wave field created by residual seismic data. Consequently, an iterative inversion scheme can be obtained is similar to that in mograms from seismic migration. The inversion results of synthetic seismograms from two different two-dimensional models prove this approaeh feasible.