This paper explores the clinical efficacy of orthodontic retention of third molars after extraction of the first or second molars. Studies show that the use of the second molar near the movement to replace the first molar, retain the third molar although need a long treatment time and higher treatment cost, but promote the gap of tissue regeneration, preserve healthy natural teeth, restore occlusal stability, but also can avoid the late repair of the first molar or second molar. In addition, the second molar after moving near the third molar is also conducive to the eruption of the third molar, maximizing the use of the third molar, to form a healthy and complete functional tooth line. Therefore, For patients with severe removal of the first or second molars, poor prognosis, severe periapical disease, and loss of the first or second molars, the treatment method of replacing the second molar for the first molar and the third molar for the second molar can be an effective treatment option.