A high-energy X-ray beam from a synchrotron radiation source, SPring-8, was used to determine the residual stress distribution below the shot-peened surface of a carbon steel plate. By using the monochromatic X-ray beam with three energy levels of 30, 60 and 72 keV, the stress values were determined by the sin(2)psi method with the side-inclination method (psi diffractometer). The stress value was estimated from the slope of the linear approximation of the relation between 26 and sin 2W in the range of sin(2)psi = 0 to 0.5. The estimated stress agreed with the distribution off the residual stress measured by removing the surface layer and repeating the X-ray measurement with Cr-Kalpha radiation. The nonlinearity of the sin(2)psi diagram can be used to estimate the distribution of the residual stress. A new method was proposed to estimate the stress value of the distributed residual stress. The new method was a combination of the side-inclination method and the iso-inclination method (omega diffractometer) to maintain the penetration depth constant. The stress value at a given penetration depth was successfully determined by the new method.