The analysis of unexplained fever in dogs and cats is mainly based on three stages. 1. Comprehensive medical history investigation and physical examination, and understanding and recording of the basic conditions of dogs and cats through questioning, palpation, etc. 2. Use non-invasive or invasive examinations, including blood routine, biochemistry, urine tests, etc. to check for differential diagnosis and rule out related causes. 3. If no diagnosis is found in the previous stage, therapeutic experiments can be attempted.