Objective: To study the clinical efficacy and prognosis of T4K appliance in the treatment of children with class-IImalocclusion in early mixed dentition. Methods: A total of 48 children with class-II malocclusion in early mixed dentition, who were treated in Shenzhen Hospital of Guangzhou University of Chinese Medicine from February 2015 to March 2017, were selected. The children were treated with T4K appliance for 6 months. The model measured values, X-ray cephalometric data, and above height, below height, below high proportion were compared between the two groups before treatment and 6 months after treatment, followed up for 3 years. The examination data of X-ray cephalometric radiographs were analyzed. Results: The overbite value, overjet value, upper arch crowding, lower arch crowding of children after six months of treatment were significantly lower than those before treatment; the upper arch width and lower arch width were significantly higher than those before treatment, the differences were statistically significant(all P<0.05). SNA angle, ANB angle, U1-SN angle and coverage of children after six months of treatment were significantly lower than those before treatment; SNB angle, L1-MP angle, U1-L1 angle and mandibular plane angle were significantly higher than those before treatment, the differences were statistically significant(all P<0.05). The above height, below height, below high proportion of children 6 months after treatment were significantly higher than before treatment, the differences were statistically significant(all P<0.05). After 3 years of follow-up, the results showed that the ANB angle and L1-MP angle were significantly lower than those 6 months after treatment(P<0.05),while the SNB angle, U1-L1 angle, the mandibular plane angle, above height, below height, below high proportion, coverage were significantly higher than those 6 months after treatment(P<0.05). Conclusion: The application of T4K appliance in the treatment of children with class-II malocclusion in early mixed dentition has better curative effect, and it is beneficial to the rehabilitation and prognosis, which is worthy of clinical promotion. [ABSTRACT FROM AUTHOR]