Abstract: Objective:To explore the predictive value of systemic immune inflammation index(SII)and fibrinogen/albumin ratio (FAR) on the prognosis of patients with advanced lung cancer undergoing first-line platinumcontaining chemotherapy before treatment.Methods:The clinical data of 260 patients with advanced lung cancer admitted to our hospital from January 2017 to December 2021 were analyzed retrospectively.The cut-off values of SII and FAR were determined by drawing the receiver operating characteristic (ROC) curve, and the patients were divided into high level group and low level group by the cut-off values of SII and FAR.The clinicopathological characteristics and total survival time of patients with advanced lung cancer with different SII and FAR expression levels were analyzed, and the factors affecting the prognosis of patients with advanced lung cancer were analyzed by univariate and multivariate Cox regression analysis.Results:The median survival time of 260 patients was 18 months, 172 patients died(66.15%)and 88 patients survived(33.85%).The areas under ROC curve(AUC) of SII, FAR and SII-FAR for predicting the prognosis of patients with advanced lung cancer were 0.730, 0.656 and 0.733, respectively.The sensitivity and the specificity were 0.616 and 0.761, 0.622 and 0.750, and 0.669 and 0.705, respectively.The tumor diameter and pleural effusion of patients in the high SII level group and low SII level group were significantly different (P< 0.05).There were significant differences (P< 0.05) in sex, age, smoking history, pathological type, tumor diameter, and treatment regimen between patients in the high FAR level group and those in the low FAR level group.The survival rate of patients in the low SII level group was higher than that in the high SII level group, and the survival rate of patients in the low FAR level group was higher than that in the high FAR level group (all P< 0.05).High level of SII was an independent risk factor affecting the prognosis of patients with advanced lung cancer (P< 0.05) and there was a positive correlation between SII and FAR (r=0.412, P< 0.001).Conclusion:The levels of SII and FAR before treatment have certain predictive value for the prognosis of advanced lung cancer patients.Patients with low levels of SII and FAR have better survival prognosis than those with high levels of SII and FAR.