The diagnostic criteria for reactive arthritis include peripheral arthritis, history of infection, laboratory tests and imaging findings. 1. Peripheral arthritis: peripheral arthritis usually develops acutely 1~6 weeks after infection, with asymmetric distribution of single or oligoarticular arthritis, which is commonly found in the knee and ankle joints, and secondly in the shoulder, wrist and elbow joints, and may manifest as swelling, pain and high skin temperature. 2. History of infection: patients may have a history of non-gonorrheal urethritis, bacterial diarrhea, and other pathogenic microorganisms such as chlamydia and salmonella. 3. Laboratory tests: routine blood tests can detect increased leukocytes and C-reactive protein, and increased blood sedimentation. Secondly, rheumatoid factor and antinuclear antibody are usually negative. 4. Imaging tests: Imaging tests are not necessary for diagnosis, but are important for differential diagnosis after evaluation of the patient’s condition, and commonly include X-rays, joint ultrasound, and magnetic resonance imaging (MRI). Reactive arthritis should be diagnosed under the guidance of a doctor, and should not be diagnosed blindly on its own, so as not to affect the condition.