In X-ray stress measurements for uni-directionally deformed surfaces such as grinding, a strongly curved diagram, so called -splitter, has been observed recently. It has been known that this is caused by the residual shear stress induced in the deformed layer by external forces. In this case it is necessary to consider this enough for ceramics and composite materials with tri-axial stress analysis. However, sufficient studies have not been done about the tri-axial stress analysis of the macro stress and micro. stress on each phase of the composite materials. The result of obtaining is as follows. 1. -splitter does not appear in the vertical direction though -splitter appears in grinding direction in WC-Co cemented carbides. The reversal of -splitter to each phase does not appear. 2. -splitter caused in WC-Co cemented carbides has a close relation in dislocation which accumulates in WC phase and phase transformation caused in Co phase. 3. The residual stress on the surface of grinding of each phase is in the state of the compression stress.