Abstract: This paper unifies the phenomenological theory of crystallography and that of kinetics, and builds a new theory based on the phase interface motion for the martensitic transformations. The interface can be described with a characteristic tensor, which is the invariant plane strain. Thus, the motion of this interface will transform the parent phase to martensite,conforming to all regulations of the crystallography such as habit plane, orientation, etc. On the other hand, the interface can be taken as an elastic and plastic layer. The characteristic tensor, functioning as strain, corresponds to certain elastic and plastic energy (work), which is exactly the friction quasi-enthalpy in the friction function during the interface moving. The interface, i.e. the invariant plane, usually is not a rational plane and is consisted of various low index facets. The number of the configuration of the facets consists the configuration entropy of the interface, which is exactly the friction quasi-entropy in the friction function. Thus, the motion of the interface will show all the kinetic behaviors such as reversibility and hysteresis during the marten-sitic transformations.