Objective To investigate the expression of prognostic nutrition index PNI combined with neutrophil / lymphocyte ratio NLR and C-reactive protein / albumin ratio CAR in patients with bone metastases and its effect on prognosis. Method A total of 200 patients with bone metastases diagnosed and treated in our hospital from January 2020 to June 2023 and followed up to December 2023 were selected as the study subjects and set as the bone metastases group while 102 healthy subjects were selected as the control group during the same period. The changes of PNI NLR and CAR in the two groups were compared. The changes of PNI NLR and CAR in different pathological features of bone metastases were observed. Spearman method was used to analyze the correlation between PNI NLR CAR and clinical features of patients with bone metastases. Multivariate Cox regression risk model was used to analyze the effects of PNI NLR and CAR on the overall survival time of patients with bone metastases. ROC curve model was drawn to analyze the predictive efficacy of PNI NLR CAR and the three combinations in predicting the prognosis of patients with bone metastases. Result PNI in bone metastatic tumor group was lower than that in control group NLR and CAR were higher than that in control group P< 0. 05 . There were statistically significant differences among different bone metastasis types combined with other site metastasis bone changes ECOG score PNI NLR and CAR of SREs P<0. 05 . Correlation analysis showed that PNI was negatively correlated with bone metastasis type combined with other site metastasis ECOG score and SREs P<0. 05 . NRI and CAR were positively correlated with bone metastasis type other site metastasis bone changes ECOG score and SREs P<0. 05 . Cox regression risk model analysis showed that decreased PNI and increased NLR and CAR were independent influencing factors for overall survival of patients with bone metastases P<0. 05 . ROC curve analysis showed that the AUC values of PNI NLR CAR and the combination in predicting the prognosis of patients with bone metastases were 0. 915 0. 766 0. 759 0. 951. Conclusion The decrease of PNI and the increase of NLR and CAR are significantly correlated with the prognosis of patients with bone metastases. Monitoring the changes of PNI NLR and CAR levels is conducive to providing references for clinical treatment.