Upper bainite bears a lath\|shaped morphology closely resembling to Widmanstɑtten ferrite as well as lath martensite.They are all the transformation products of over\|cooled austenite and each has an irrational FCC/BCC interface very near to the close\|packed plane (111)\-f.The step\|dislocation structure of the lath martensite interface has been verfied in an atomic scale by high resolution electron microscope.The interface structure models of lath martensite and Widmanstɑtten ferrite have been improved on the basis of the epitaxial interface dislocation theory as combined with their experimental crystallography.The two models represent all the possible interface categories for the epitaxial interface conjugated along the close\|paked (111)\-f/(011)\-b plane,being compatible with their respective growth kinetics.It appears that there is no another model for upper bainite interface except the preceeding ones.The type of the bainite interface will be verified by experiments.Investigations in the present work show that accurate experiments and relevant analyses of the interface structure combined with a given variant of crystallography may be the crucial routine for determining the interface structure and in turn identifying the growth mechanism of the bainite.F C C/ B C C Interface Structure and Gro wth Mechanismof Lathshaped Tr