Abstract: X-ray diffraction analysis of the nanocrystalline pure aluminum sample prepared by spark plasma sintering was carried out, and fully annealed silicon powders were used as the standard sample to separate the instrument widening. The method of calculating average grain size of nanocrystalline pure aluminum sample by using 'integral width method' after extracting the physical widening was proposed. The results show that the average grain size of the test pure aluminum sample is 73.7 nm, and it has reached the nanometer scale.