Objective To investigate the expression and significance of Forkhead Box M1 (FOXM1) in the process of repair of acute lung injury (ALI) in mice with severe acute pancreatitis (SAP). Methods BALB/c mice were randomly divided into a sham group (10 mice) and a model group (50 mice), and the model group was then randomly divided into 5 subgroups, namely 1-day, 3-day, 7-day, 10-day and 14-day subgroups (10 in each). The SAP/ ALI model was induced by the method of intraperitoneal injection of caerulein. The pathological changes of the lung tissues and the pulmonary microvascular permeability were observed. The water content of the lung tissues and the serum amylase level were detected. In addition, qRT-PCR and Western blot were used to detect the FOXM1 mRNA and protein expression levels respectively at different time points during the repair process of lung injury in the SAP/ ALI mice. Finally, the correlation between FOXM1 protein expression and pulmonary microvascular permeability was analyzed. Results Compared with the sham group, the morphology of the lung tissues changed in the model group at each time point (on days 1, 3, 7, 10 and 14), the pathological changes were alleviated over time (P < 0.05). The changes of serum amylase level, pulmonary vascular permeability and water content of the pulmonary tissues were similar with the change of pathological scores after lung injury. At the same time, the expression of FOXM1 mRNA in the lung tissues had an obvious dynamic evolutional rule. The expression of FOXM1 mRNA decreased on the 1st day after modeling, then increased gradually from the 3rd day, and reached the peak on the 7th day, gradually restored on the 10th day, and returned to the baseline on the 14th day. Moreover, FOXM1 protein expression level also presented the similar rule. There was a negative correlation between the expression of FOXM1 protein and the pulmonary microvascular permeability (P < 0.05). Conclusions FOXM1 may play an important role in the repair of pulmonary blood-gas barrier.