In the outpatient clinic, we often come across some patients with knee pain, popping and ringing, diagnosed as “discoid meniscus injury” by MR examination. In fact, discoid meniscus is a kind of meniscus growth and development deformity, and the incidence of lateral meniscus is higher than that of medial meniscus. Normal meniscus is C-shaped or O-shaped covering the periphery of the cartilage surface of the tibial plateau, whereas discoid meniscus is a complete disk, covering the entire cartilage surface of the plateau. Therefore, the discoid meniscus is more susceptible to extrusion under the influence of minor trauma, resulting in injury. After injury, the discoid meniscus is often compressed in the joint space, resulting in knee pain, popping, interlocking, and a feeling of being stuck. Discoid meniscus is not visualized on plain X-ray and can be definitively diagnosed by MR examination. Uninjured discoid meniscus found on arthroscopy or inadvertent MR examination mostly does not require surgical treatment. Early arthroscopic treatment is recommended for symptomatic discoid meniscus injuries to avoid repeated abrasion of the cartilaginous surfaces of the joint by the injured meniscus, which can lead to secondary injuries as well as osteoarthritis. Depending on the specific situation of the arthroscopic meniscus injury, meniscus repair or meniscus suture is used in the operation, in order to achieve the purpose of relieving joint pain and restoring joint function.