Objective To analyze the factors influencing prognostic death in elderly patients with lung cancer complicated with malignant pleural effusion (MPE) and to observe the progression-free survival (PFS). Methods The clinical data of 244 elderly patients with lung cancer complicated with MPE admitted to First Hospital of Qinhuangdao from January 2023 to December 2024 were collected. According to the 6-month prognostic survivals, the patients were divided into a survival group (n=172)and a death group (n=72). The two groups were compared in the prognostic nutritional index (PNI), SELECT prognosis prediction model risk grading, epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) targeted therapy, therapeutic efficacy, and other general data. SPSS 25.0 was used for data analysis. According to the data type, t test, Chi-square test, or Mann-Whitney U test was used for comparison between groups. Multivariate logistic regression analysis was used to evaluate the factors influencing prognostic death in elderly patients with lung cancer complicated with MPE. Kaplan-Meier method was used to plot progression-free survival curves, and log-rank test was used to evaluate differences in PFS. Results The proportions of patients with PNI ≥ 45 and those receiving EGFR-TKI targeted therapy were lower in the death group than those in the survival group, while the proportion of malnutrition and risk grading of SELECT prognostic prediction model were higher in the death group than in the survival group (P<0.05). Multivariate logistic regression analysis (stepwise conditional regression) revealed that malnutrition (OR=4.433,95%CI 2.335-8.414; P<0.05) and high risk of SELECT prognosis prediction model (OR=4.850,95%CI 2.047-11.489; P<0.05) were risk factors for prognostic death in elderly patients with lung cancer complicated with MPE, and PNI ≥ 45 (OR=0.324,95%CI 0.152-0.691; P<0.05) and EGFR-TKI targeted therapy (OR=0.257,95%CI 0.124-0.535; P<0.05) were protective factors. Progression-free survival curve analysis showed that median PFS was longer in patients with PNI ≥ 45 than in those with PNI <45, shorter in those with malnutrition than in those without malnutrition, shorter in those with high risk of SELECT prognosis prediction model than in those with low and medium risk, and longer in those receiving EGFR-TKI targeted therapy than those not receiving EGFR-TKI targeted therapy; all differences were statistically significant (P<0.05). Conclusion Patients with high risk shown in the SELECT prognostic prediction model and concurrent malnutrition have shorter PFS and a higher risk of prognostic death. High PNI levels and EGFR-TKI targeted therapy may be beneficial in prolonging the PFS and reducing the risk of prognostic death, providing a reference for the clinical management of elderly lung cancer patients with MPE.