Objective To recognize the risk factors of unplanned re-interventions within 30 days after pediatric cardiac surgery and evaluate the outcome of re-interventions. Methods We retrospectively analyzed the clinical data of 202 children in Fuwai Hospital between January 1, 2015 and August 31, 2017. There were 115 males and 87 females at average age of 32.4 months with range of 3 days to 14 years. Results There were 202 children who underwent unplanned re-intervention during 30 days post-operation, including 54 re-adjustments of pulmonary blood flow, 34 re-corrections for residual cardiac abnormalities, 28 cardiopulmonary resuscitations, 38 for coagulation problems, 19 pericardial drainages, 11 palliative re-operations to deliver heart load and 6 diaphragmatic folds and 12 others. The mortality rate among children who underwent unplanned re-inventions after cardiac surgery was 10.9% (22/202). It was much higher than those free from re-interventions (0.7%). Time of mechanical ventilation was 284.3 (11–2 339) h, and mean ICU stay was 17.7 (1–154) d, significantly longer than those free from re-interventions at the same period. Conclusion Unplanned re-interventions after pediatric cardiac surgery is associated with higher mortality rate and longer recovery time. Early identifying risk factors and re-intervention can reduce the complications and improve the prognosis.