The purpose of this study is to investigate the incidence and risk factors for developing proximal junctional kyphosis (PJK) in Lenke 3 adolescent idiopathic scoliosis patients following all-pedicle instrumentation and correction after a minimum of two years follow up. From June 2016 to June 2019, medical records of Lenke 3 AIS patients were reviewed, including posteroanterior and lateral whole spine X-ray films preoperatively, postoperatively (8-10 days after surgery), and after 2 years of follow-up. Demographic data, as well as radiologic parameters, were evaluated. Binary logistic Regression analysis was performed to detect the risk factors of PJK. The current study recruited 50 Lenke 3 AIS patients with a minimum follow-up of 2 years. Three (6%) of 50 cases had PJK, no patient required revision because of PJK. Binary logistic regression showed that Larger preoperative thoracic kyphosis > 43°, larger preoperative lumbar lordosis and larger postoperative lumbar lordosis > 45° were the main risk factors of PJK [Odds Ratio (OR) = 0.429,0.863 and 1.024 respectively]. The incidence of PJK was 6%, greater preoperative thoracic kyphosis > 43°, greater preoperative, and postoperative lumbar lordosis > 45° were the main risk factors for PJK. Careful long-term follow-up should be performed to identify risk factors and reduce the occurrence of PJK.