During plastic deformation and strain-induced martensitic transformation (SIMT), the irreversible viscoplastic work and latent heat can act as a heat source in TRIP steel. To obtain expected mechanical properties in the steel, a deep understanding on the temperature dependency of SIMT is indispensable. At a microstructural scale, unavoidable dislocations induced by martensitic transformation can affect its plastic deformation behavior with a length scale effect. In this study, a heat conduction equation to include the martensitic transformation coupled with size-dependent crystal plasticity based on a notion of microforce is derived. Then, FE simulation with cellular automata on infinite monocrystal TRIP steel is performed at various strain rate.