Cu/Cu2O powder nanocomposites (PNCs) were successfully synthesized by colloidal solution method. To investigate the influence of oxidant agent concentration on the crystallite size and lattice constant of the PNCs, X-ray diffraction (XRD) was utilized to collect the database for crystal growth analysis. Due to the imperfect crystal growth, the Nelson-Riley function and the Williamson-Hall method were used to confirm the precise values of the PNCs. The Rietveld refinement method based on the XRD pattern was used. The XRD results show that the diffraction peaks were mainly assigned to the cubic structure, in good agreement with the ICDD standards. Furthermore, the change in oxidant agent concentration led to a very small change of microstrain in the peaks of Cu/Cu2O PNCs. Using these methods can aid in the precise study of the crystalline structure of the material, which can then be calculated to adjust the influencing conditions during the synthesis of the material.