ObjectiveTo analyze the clinical characteristics of acute pancreatitis (AP) complicated with pulmonary infection and to explore the value of BISAP, APACHEⅡ and CTSI scores combined with C-reactive protein (CRP) in early diagnosis and prognosis of AP complicated with pulmonary infection.MethodsFour hundreds and eighty-four cases of AP treated in the Affiliated Hospital of North Sichuan Medical College from January 2018 to January 2020 were selected. After screening, 460 cases were included as the study object, and the patients with pulmonary infection were classified as the infection group (n=114). Those without pulmonary infection were classified as the control group (n=346). The baseline data, clinical characteristics, laboratory test indexes, length of stay, hospitalization cost, and outcome of the two groups were collected, and the risk factors and early predictive indexes of pulmonary infection in patients with AP were analyzed.ResultsHospitalization days and expenses, outcome, fluid replacement within 24 hours, drinking, smoking, age, APACHEⅡ score, BISAP score, CTSI score, hemoglobin (Hb), albumin (ALB), CRP, procalcitonin (PCT), total bilirubin (TB), lymphocyte count, international standardized ratio (INR), blood glucose, and blood calcium, there were significant differences between the two groups (P<0.05). There were no significant difference in BMI, sex, recurrence rate, fatty liver grade, proportion of patients with hypertension and diabetes between the two groups (P>0.05). The significant indexes of univariate analysis were included in multivariate regression analysis, the results showed that Hb≤120 g/L, CRP≥56 mg/L, PCT≥1.65 ng/mL, serum calcium≤2.01 mmol/L, BISAP score≥3, APACHEⅡ score≥8, CTSI score≥3, and drinking alcohol were independent risk factors of AP complicated with pulmonary infection. The working characteristic curve of the subjects showed that the area under the curve (AUC) of CRP, BISAP score, APACHEⅡ score and CTSI score were 0.846, 0.856, 0.882, 0.783, respectively, and the AUC of the four combined tests was 0.952. The AUC of the four combined tests was significantly higher than that of each single test (P<0.05).Conclusions The CRP level, Apache Ⅱ score, bisap score and CTSI score of AP patients with pulmonary infection are significantly higher, which are closely related to the severity and prognosis of AP patients with pulmonary infection. The combined detection of the four items has more predictive value than the single detection in the early diagnosis and prognosis evaluation of AP complicated with pulmonary infection. Its application in clinic is of great significance to shorten the duration of hospitalization and reduce the cost of hospitalization and mortality.