The phase transition of Copper-tungsten films deposited on Si (100) and Al2O3 substrates took place by means of in situ annealing in vacuum chamber at different temperatures. X-ray diffraction (XRD) and the polarization phase shift technique were employed to characterize the microstructure and residual stress of Cu-W films, respectively. The results indicated that the two successive but distinctive stages of phase transition appeared with the change of annealing temperatures, i.e., W (Cu) solution formation and two-phase crystalline (W and Cu) structure formation. The relationship between phase transition and residual stress was investigated, the tensile stress was caused during phase transition, whereas it was released with crystalline growth.