Gallium nitride (GaN) thin films are typically obtained on foreign substrates. Hetero-epitaxial growth of GaN leads to high density of threading dislocations, which poses a significant challenge to promote high-performance electronic device and photoelectric device based on these films. This research used Ar-ion implantation pretreatment on sapphire substrates to induce high-quality nucleation, reducing the dislocation density in GaN epitaxial layers. By optimizing the dosage of Ar ions, it was found that when the Ar ion dosage was 1×10¹¹ cm^-2, the screw dislocation density was 5.26×10⁷ cm^-2, and the edge dislocation density was 1.95×10⁸ cm^-2, the total dislocation density decreased by 65% compared to GaN grown on traditional sapphire substrate. Photoluminescence spectra realized that the optical performance of the GaN epitaxial layer with induced nucleation was also improved. In contrast to the untreated sample, the photoluminescence strength increased by 152%. Therefore, all above results indicate that the Ar ion induced nucleation technique proposed in this study is a simple and effective method that can be used to improve the crystal quality of GaN layers. This is of great significance for achieving high-efficiency GaN-based LEDs and high-performance electronic devices.