Abstract: Since most wells used for cross-well exploration are horizontal wells,not declined wells,original issues of cross-well seismic have converted from2 D to 3D.But issues of kinematic forward modeling in complicated structures cannot be solved through conventional forward simulation methods such as trial ray method and segmentally-iterative ray tracing method.Therefore,program of 3D block forward modeling is raised from3 D block and segmentally-iterative ray tracing method.Programs of 3D block forward modeling for cross-well seismic are written with Qt and VC++ 6.0in this paper,fundamentals of 3D block forward modeling incross-well seismic has been actualized.An analysis of seismic forward model about many complicated cross- well models has been made by using its procedure.The results of forward computerized methods show that methods and procedure are applicative.