This paper shows the effects of the XRD experiments on the different residual stresses of polycrystalline diamond compacts by XRD. Analyzing these effects in terms of the principle that field phase takes place coherent and incoherent diffraction reaction with X-ray, and applying to the Conpton- Youxun Wu’s theory that scattering intensity increases with the increase of sin/. This paper builds a mathematic model of semi-quantitative characterization of the residual stresses of PDC. For the XRD spectral line chart of PDC with known ranking residual stresses, diffraction reaction fails to happen in PDC when it is in low-angular domain, I can be expressed as: I = K() / + I0, that means the XRD spectral line can be regarded as a beeline. Calculating all the K() values of PDC with the same specification but with the different surface of residual stresses according to the formula, this paper completes the semi-quantitative characterization of residual stresses of PDC with the same specification.