The first step in diagnosis is clinical examination to detect and find the site, manifestations and symptoms of the patient’s deformity and the duration of the deformity according to the patient’s chief complaint. However, there are still many symptoms and manifestations that require more detailed examination of the patient with the help of various medical devices and instruments in order to further analyze the cause of the deformity, the mechanism causing the deformity, and to collect enough available information for the diagnosis. The second step is to analyze and categorize the collected data to clarify all the deformity problems of the patient and classify these problems to basically determine the cause and mechanism of the deformity. The third step is to determine the treatment plan. The treatment goals, objectives, indications, specific steps and predicted outcomes are clarified. Once again, the time required for treatment, the cost and the possible problems after treatment (i.e., prognostic analysis) need to be repeatedly emphasized and documented in the case. The basic process of diagnosis is as follows: 1. General information Include the patient’s chief complaint, past medical history, current medical history, and the patient’s current systemic status, such as development, nutrition, systemic diseases, adverse perceptions, and psychological reactions. 2.Clinical examination including the patient’s facial examination, orthodontic clinical examination, and special examination, such as X-ray examination, etc. 3.Comprehensive analysis including model analysis, functional analysis, X-ray cephalometric analysis, psychological analysis, etc. 4.Diagnosis General diagnosis includes four elements: ① List the problems. (2) Classification of deformity, including Angle classification, etiology classification, etc.; (3) Mechanism leading to deformity. Underdevelopment of the maxilla, overdevelopment of the mandible, excessive anterior tilt of the teeth, etc.; (4) Factors causing the malocclusion, such as heredity, bad habits and trauma, etc. If the diagnosis is not clear at the moment, “diagnostic treatment” can be carried out first, and the diagnosis can be determined after the initial treatment.