Melasma is a complex and diverse skin disease of increased pigmentation that occurs on the face and is difficult to treat. Due to the relative lag of its basic research, it has caused blindness and uncertainty in its treatment. The literature reports a wide range of treatment methods with poor reproducibility. At present, the Q-switched Nd:YAG laser with low energy density and large spot has been applied to the clinical treatment of melasma in the Department of Cosmetic Dermatology of our hospital, and has achieved good recent efficacy. The basic principle of Q-switched Nd:YAG laser in treating pigmentation disease is that Q-switched laser can release huge energy to the target tissue in an instant, causing the target, that is, the pigment particles of melasma, to be crushed into very small particles and then cleared by macrophages in the patient’s tissue, while the surrounding tissue is No damage. Studies have shown that there is no significant difference in the efficacy of Q-switching for treating epidermal, dermal and mixed types of melasma. In conclusion, the recent efficacy of low-energy density, large spot Q-switched laser treatment for melasma is still acceptable and the side effects are small, so it is an effective means of external treatment of melasma in clinical practice. However, the deeper mechanism of its effectiveness and the interrelationship between efficacy, side effects and energy density need to be further studied from basic research, and the long-term efficacy needs further observation.