The use of low grade, high impurity copper concentrate has made the copper smelting process increasingly complex. As the composition of copper slag changes, controlling slag characteristics is essential to maintain process efficiency and improve slag matte separation. Al2O3 is one of the major gangue elements in the copper smelting process and has an important impact on the physicochemical properties of copper slag. However, the effect of high Al2O3 content on copper smelting has been less studied. In this study, the effect of different Al2O3 contents on the phase and structure of copper slag and the modification of high-alumina copper slag by adjusting the Fe/SiO2 ratio and CaO addition were investigated by using chalcopyrite concentrate as raw material. The results showed that the increase in Al2O3 content promoted the formation of spinel and complicated the slag structure. Increasing the Fe/SiO2 ratio and CaO addition can simplify the slag structure but increase the production of high melting point phases. Reasonable proportion of Fe/SiO2 ratio and CaO addition can effectively reduce the loss of copper in high-alumina copper slag. The results of the study provide a theoretical basis for selecting reasonable process parameters for the smelting of high-alumina copper concentrates and recovering secondary resources containing Al2O3.