Abstract: Ethanol solutions are very important objects to be detected in liquid security detection, and accurate analysis of the concentration is advantageous to the liquids treat level assessment and the follow-up inspection. Diffraction peak position may also become an important physical parameter, which provides valuable identification information for liquids classification. Experiments were done on ethanol solutions with different concentrations, using the X-ray diffraction (XRD) method. In order to improve the accuracy of the diffraction spectra measurements, geometric calibration method was proposed based on the error analysis of the actual XRD system. The relationship was found between the diffraction peak position and the concentration after geometric calibration and spectra correction.