Objective To explore the effects of ultrafiltration technique in preventing and relieving pulmonary injury in children undergoing open heart surgery and cardiopulmonary bypass (CPB).Methods Thirty cases with congenital heart defects were divided into a control group and an experimental group. In the control group, conventional cardiopulmonary bypass was used without ultrafiltration; while in the experimental group, cardiopulmonary bypass with balanced ultrafiltration and modified ultrafiltration were used. Pulmonary static compliance (Cstat), airway resistance (Raw), alveolar-arterial oxygen difference (A-a DO2), hematocrit (HCT), serum albumin (Alb), interleukin-6 (IL-6), endothelia-1 (ET-1) and thromboxane (TXB2) were measured. Results The pulmonary function was improved, HCT and serum albumin concentrations were increased, and some harmful medium-size solutes were decreased in the experimental groups compared with the control group.Conclusions Combination of balanced ultrafiltration with modified ultrafiltration can effectively concentrate blood, exclude harmful inflammatory mediators, and attenuate lung edema and inflammatory responsive pulmonary injury.