Objective To compare the effectiveness of early versus delayed closed reduction and percutaneous Kirschner wire fixation in the treatment of pediatric supracondylar humerus fractures. Methods A retrospective analysis was conducted on 468 children with supracondylar humerus fractures, who were admitted between January 2020 and December 2023 and met the inclusion criteria. Among them, 187 children were treated during 12 hours after injury (early operation group) and 281 were treated after 12 hours (delayed operation group). There was no significant difference between the two groups (P>0.05) in the gender, age, injury mechanism, fracture side and type, while there was significant in interval from injury to operation (P<0.05). The operative outcomes, including the operation time, intraoperative blood loss, hospital stay, fracture healing time, elbow function (assessed by Flynn criteria) at 3 months after operation, and complications, were compared. Results Compared to the delayed operation group, the early operation group demonstrated significantly shorter operation time and less intraoperative blood loss (P<0.05). There was no significant difference in the length of hospital stay between the two groups (P>0.05). All children were followed up 3-12 months. The follow-up time was (6.7±2.9) months in the early operation group and (6.9±2.8) months in the delayed operation group (P>0.05). There was no significant difference in the fracture healing time between the two groups (P>0.05). At 3 months after operation, the early operation group exhibited superior Flynn elbow functional outcomes to the delayed operation group (P<0.05). In the early operation group, there was 1 case of fracture non-union, and 3 cases of cubital varus deformity after operation. In the delayed operation group, there was 1 case of nerve injury, 7 cases of fracture non-union, and 12 cases of cubital varus deformity after operation. There was a significant difference in the incidence of complications between the two groups (P<0.05). One case of the early operation group and 10 cases of the delayed operation group were undergone secondary operation, sowing no significant difference in the incidence of secondary operation between the two groups (P>0.05). Conclusion For pediatric supracondylar humerus fractures, early closed reduction and percutaneous Kirschner wire fixation can reduce operation time, minimize intraoperative blood loss and postoperative complications, and improve the functional recovery compared to delayed operation.