We utilize slow highly charged ions of Xeq+ and Pbq+ to irradiate GaN crystal films grown on sapphire substrate, and use X-ray photoelectron spectroscopy to analyze its surface chemical composition and chemical state of the elements. The results show that highly charged ions can etch the sample surface obviously, and the GaN sample irradiated by highly charged ions has N depletion or is Ga rich on its surface. Besides,the relative content of Ga—Ga bond increases as the dose and charge state of the incident ions increase. In addition, the binding energy of Ga 3d5/2 electrons corresponding to Ga—Ga bond of the irradiated GaN sample is smaller compared with that of the Ga bulk material. This can be attributed to the lattice damage, which shifts the binding energy of inner orbital electrons to the lower end.