In this paper, the p-i-n multiple-layer Al_(x)Ga_(1-x)N sample with high Al (x>0.45) content was measured by the triple-axis X-ray diffraction measurement. The strain state and screw dislocation density of each layer in Al_(x)Ga_(1-x)N epitaxial layers were determined by RSM (reciprocal space map) method. Then, the PV function was used to fit the rock curves separated from the RSM. At last, the strain and the screw dislocation density of each layer were accurately calculated by fitting these rock curves.