The thermal conductivity of W-Cu composites is affected by the position where they were placed in during infiltrating. The W-Cu composites after infiltrating were kept at a certain temperature for some hours with the protection of hydrogen and then cooled down to room temperature by different means. By X-ray diffraction experiment, tungsten phase is found to be under compression and copper phase under tension. The value of the residual stresses increases with the cooling rate, while the thermal conductivity, inversely. The coefficient of thermal expansion(CTE) mismatch of tungsten and copper led to the significant amount of thermal stresses at the interface and low thermal conductivity. The effect of the residual stresses on the thermal conductivity, as well as its mechanism was analyzed.