The best time for orthodontic treatment of deep overjet should be at the end of the replacement period, around 11~15 years old. Deep overjaw is a kind of malocclusion. During the period when milk teeth are replaced by replacement teeth, the teeth change the most, and there are abnormal teeth arrangement and misalignment of occlusal relationship. It is clinically recognized that the end of the replacement period is the best time to correct deep overjet, as the jaw and face are in a rapid growth stage, the teeth recover and move faster, and the jawbone plasticity is correspondingly stronger, so the correction takes less time and the effect of correction is more obvious. Early correction of deep overjet can minimize the impact on the temporomandibular joints, but missing the optimal age for correction may increase the correction time, affect the correction effect, and even affect the joint function as the teeth become more worn.