Abstract: Cementite near the interface in 321/Qd370qD explosive welding is analyzed by transmission electron microscopy.The results show that there is a lot of cementite in austenitic side of the interface, and a lot of sub-lamellae exist in the cementite beside the interface.These sub-lamellae are about several nanometers and parallel each other.Some sub-lamella groups cross approximately 70.5° and accord with definite crystal tropism relation, which coincide each other when they circumrotate 180° with 110_α as axis or with 002_α as axis. Thus, a new sub-lamella group can easily grow beside another sub-lamella group.The crystal tropism relation of adjacent sub-lamellae may be applied to adjacent pearlite groups that maybe exist the above relation.