Abstract: The content of minerals in feldspar can be calculated by chemical analytical results, but the analytical process is long and the calculation process is complex. Moreover, slice position could affect the result of feldspar content determined by optical microscopy. Feldspar samples were quantitatively analyzed using the Rietveld method in HighScore software. This method can effectively reduce the effect of diffraction peak overlap and correct the diffraction intensity error caused by the preferred orientation. The accuracy of the method is superior to the reference method (RIR method). The quantitative analysis results of the samples are close to the results of the adiabatic method, and the relative deviation is less than 1.69%. Compared to the mineral content by conversion from chemical composition, the absolute error is less than 5%, which meets the allowable error provided by DZ/T 0130-2006. As proved by first grade standard materials of potassium feldspar, the absolute error is less than 1%. The results of quantitative analysis of the feldspar show that the X-ray diffraction full-spectrum fitting method is simple and the analytical quality meets the quality requirements of the relevant standard for the diffraction analysis. It is feasible to analyze rock mineral content in geological samples using this method.