We consider in this paper a straight dislocation moving uniformly parallel to the planar phase boundary in a two phase medium. We take a moving coordinate system, in which the dislocation is relatively at rest, and extend the general anisotropic elastic theory of dislocation to this coordinate system. We employ the Green function method in elastic theory to treat the phase boundary, thus obtain the total elastic field produced by this moving dislocation and the "image force" acting on it. Our theoretical method is applicable in general, it can be used to consider the interaction between this dislocation and other lattice defects, and mechanical properties of the two phase medium.