〔Abstract〕 Objective To study the optimal energy density of Q-switched Cr, Er:YSGG laser,which wavelength is 2.79 μm, on enamel at nanosecond time scale by exploring the laser ablation threshold and the optimal energy density of laser treatment of enamel and recording the change of enamel temperature during the process. Methods Q-switched nanosecond pulsed Cr, Er:YSGG laser was used to treat the surface of 5 groups′enamel samples with different energy density. The surface morphology was observed by Field emission scanning electron microscopy. Subsequently Ablation threshold and energy density of each group were calculated. Energy dispersive X-ray spectroscopy was employed to detect the chemistry ingredients. Real-time monitoring and recording of temperature changes during the action of Cr, Er:YSGG laser were also recorded by a high-performance infrared camera. Results The laser ablation threshold and the optimal energy density interval of enamel with laser treated were founded and the change of enamel surface temperature corresponding to different laser energy density at low energy was collected. Conclusion The treatment of enamel with Q-switched nanosecond pulse Cr,Er:YSGG laser is fast and effective, clean and pollution-free,which avoids thermal damage to enamel and surrounding tissues including dental pulp,improves the treatment safety and provides research basis for the clinical application of nanosecond laser in oral cavity.