Acne is a chronic inflammatory skin disease of the hair follicles and sebaceous glands caused by multiple factors, which occurs in the seborrheic areas. It is most commonly seen on the face of adolescents, especially in moderate to severe acne, which affects the appearance and creates a sense of low self-esteem. Traditional treatments for inflammatory acne are usually topical creams or oral antibiotics. Although they can reduce the symptoms to a certain extent, they have a long course of treatment, many contraindications, and are prone to adverse reactions and drug resistance. Phototherapy for inflammatory acne is an advanced, purely physical treatment technique with good efficacy, little pain and minimal side effects, mainly due to local stimulation and burning, which can be solved by applying cold compresses. The indications are for all patients with inflammatory acne with non-photosensitive skin. The photonic acne treatment instrument emits 420nm light, a high-energy blue light with a specific spectrum, which can penetrate the skin and act on the porphyrins in the sebaceous glands. It can also promote the recovery of acne inflammation, accelerate the fading of pigment and scar repair without side effects, and greatly reduce the chances of acne scarring after treatment. Clinical observation found. The earlier the treatment, the faster the skin improvement and the more obvious the effect. We found that acne treatment has a positive correlation trend with the number of treatments and results. To achieve the best results, a minimum of 5-6 treatments are required, usually 1-2 treatments per week. In conclusion, the application of 420nm photon therapy for patients with moderate to severe acne is an effective treatment for inflammatory acne without any interference with normal life and studies during the treatment period.