Objective To explore the application of serum interleukin-7 （IL-7）， lactate dehydrogenase/albumin （LDH/ALB）， and soluble leukocyte differentiation antigen subtype 14 （sCD14-ST） in the diagnosis and disease assessment of chronic obstructive pulmonary disease （COPD） with pulmonary infection （PI）. Methods A total of 109 patients with COPD complicated by PI admitted to the hospital from June 2022 to June 2024 were included in the infection group. Additionally， 100 patients with uncomplicated COPD who visited the outpatient department during the same period were included in the control group. Both groups were incorporated into the training set. We compared the general characteristics， IL-7 levels， LDH/ALB ratios， and sCD14-ST levels between the infection group and the control group. Receiver operating characteristic （ROC） curve analysis was performed to evaluate the diagnostic value of these indicators in COPD complicated with PI. Patients in the Infection Group were divided into mild （n = 27）， moderate （n = 49） and severe （n = 33） subgroups based on the pneumonia severity index （PSI）. The IL-7， LDH/ALB， sCD14-ST levels and PSI of the three subgroups were compared， and Pearson's correlation analysis was conducted to analyze the relationship between IL-7， LDH/ALB， and sCD14-ST levels and PSI. Additionally， 59 patients with COPD complicated by PI and 50 patients with COPD alone admitted to the hospital between July 2024 and December 2024 were selected for the validation set to construct a nomogram model. Results The age， duration of COPD， history of diabetes， long-term use of antibiotics， mechanical ventilation status and length of hospital stay in the infection group were all higher than those in the conventional group （P < 0.05）. The levels of IL-7， LDH/ALB and sCD14-ST in the infection group were all higher than those in the conventional group （t = 4.551， 4.510， 4.329， P < 0.05）. The results of multivariate logistic regression analysis showed that IL-7， LDH/ALB， and sCD14-ST were all independent risk factors for COPD combined with PI （P < 0.05）. The combined diagnostic value of IL-7， LDH/ALB， and sCD14-ST for COPD combined with PI is higher than that of a single indicator diagnosis. The AUCs of serum IL-7， LDH/ALB， and sCD14-ST for COPD combined with PI alone and in combination are 0.711， 0.666， 0.700， and 0.856， respectively. The AUC of combined diagnosis was higher than that of individual diagnosis （Z_{IL-7~combined} = 4.877， Z_{LDH/ALB~combined} = 5.279， Z_{sCD14-ST~combined} = 4.371， P < 0.05）. The Kappa test showed that the Kappa values of IL-7， LDH/ALB， sCD14-ST and the combined diagnosis were 0.405， 0.265， 0.311 and 0.551 respectively. Levels of IL-7， LDH/ALB， and sCD14-ST in the severe subgroup were significantly higher than those in the moderate and mild subgroups， and levels in the moderate subgroup were significantly higher than those in the mild subgroup （P < 0.05）. PSI was higher in the severe group than in the mild and moderate groups， and was higher in the moderate group than in the mild group （P < 0.05）. Pearson correlation analysis revealed positive correlations between the levels of IL-7， LDH/ALB， sCD14-ST and disease severity in COPD patients with PI （r = 0.390， 0.444， 0.372， P < 0.001）. The risk factor selection model based on multifactor logistic regression demonstrated good predictive value for COPD with pulmonary infection. The AUC values for the training and validation sets were 0.82 （0.75 ~ 0.88） and 0.78 （0.66 ~ 0.90）， respectively. Calibration curves indicated that predicted values closely matched actual outcomes （P > 0.05）. The decision curve indicated a high positive net benefit at thresholds ranging from 50% to 100%. Conclusions The combination of IL-7， LDH/ALB， and sCD14-ST has high diagnostic value for COPD complicated with pulmonary infection. Furthermore， the levels of these three indicators are positively correlated with disease severity， which may provide a basis for clinical assessment of patient condition.