Abstract:in the treatment of Tonnis type Ⅲ and Ⅳ developmental dysplasia of the hip(DDH) of 18-24-month-old children. Methods A retrospective analysis was conducted on the clinical data of 47 children(56 hips) of 18-24-month-old with Tonnis type Ⅲ and Ⅳ DDH treated in Xuzhou Childrens Hospital from January 2015 to January 2018. The incidence of residual acetabular dysplasia(RAD) was obtained by measuring acetabular index(AI) and center edge angle(CEA). The therapeutic efficacy was evaluated according to Severin imaging evaluation and Mckay classification of the hip joint function. Kalamchi-MacEwen classification was used to assess avascular necrosis of fomoral head(AVN) on X-ray films. Results The average follow-up was(30.98±1.07) months for 47 children. There was a significant difference in AI index between OR group and OR+SIO+FO group(P＜0.05). CEA value in OR group was significantly different from those in OR+SIO group and OR+SIO+FO group(P＜0.05), respectively. There were no significant differences in the incidence of RAD, the excellent and good rate in Severin imaging evaluation and McKay classification of hip joint function and the rate of AVN among three groups(P＞0.05). Conclusion In the treatment of Tnnis type Ⅲ and Ⅳ DDH in 18-24-month-old children, the three different surgical methods can obtain a good short-term prognosis. However, the operation of open reduction combined with Salter pelvic osteotomy and femoral osteotomy has a better effect in improving AI and CEA.