The structural characteristics and composition of alunite in the Zijinshan gold-copper deposit were studied by infrared absorption spectroscopy and X-ray powder diffraction analysis. The results show that infrared spectral absorption peaks, the growth degree of crystal faces (006) and (004）, and crystal cell parameters of the alunite display gradually decreasing trend from the crater to northwest along the metallogenic belt. Combined with electron probe analysis results, we go further and obtain that the alunite mainly belongs to potassium alunite, and the characteristics of infrared spectra and XRD of the alunite mainly have relation to the content of potassium of the alunite in different parts of volcanic mechanism. Near the crater, with higher temperature, it is helpful for the isomorphism replacement between sodium and potassium, the content of sodium is higher and the content of potassium is lower relatively in the alunite; and away from the crater, the temperature is relatively lower, it is against the isomorphism replacement between sodium and potassium, the content of sodium is lower, and the content of potassium is higher relatively in the alunite.