Objective:To investigate the prognostic relationship between serum KL-6 level and rheumatoid arthritis(RA)combined with interstitial lung disease(RA-ILD).Methods:In Affiliated Hospital of Inner Mongolia Medical University from January 2018 to January 2021,seventy patients with RA were selected and divided into RA-ILD group(34 cases)and RA(36 cases)accord-ing to whether they were complicated with ILD,clinicopathological characteristics of the two groups of patients were analyzed by uni-variate analysis,focusing on the comparison of the expression level of KL-6 in the serum of the two groups and the correlation analysis with laboratory indexes,lung function and imaging,multivariate Logistic regression analysis risk factors affecting RA-ILD.Results:There were significant differences in gender,smoking history,age,age of onset,course of disease,DAS28,KL-6,WBC,UA,RF,anti-CCP antibody,TLC%Pred and DLCO%Pred between the two groups(P<0.05).In RA-ILD group,the proportion of clinical symp-toms was more prominent,joint pain was more prominent,and the thickening of pleural adhesion was more prominent on HRCT;Spearson correlation analysis showed that the level of serum KL-6 in RA-ILD group was significantly negatively correlated with TLC%Pred,VC%Pred and DLCO%Pred(P<0.05);there was a significant positive correlation with RF and anti-CCP antibody levels(P<0.05);there was no significant correlation with FEV1%Pred and FEV1/FVC(P>0.05);expression level of KL-6 in RA-ILD group was significantly higher than that in RA group before treatment,and there was no significant difference after treatment(P>0.05);Fol-lowed up for one year,six patients died in RA-ILD group.The expression level of KL-6 in death group was significantly higher than that in non death group(P<0.05);multivariate Logistic regression analysis showed that old age,male,smoking,increased anti CCP antibody and KL-6 were independent risk factors for RA-ILD(P<0.05);the maximum area under the ROC curve predicted by serum KL-6 was 0.802,the 95%CI was 0.743～0.866,the sensitivity was 0.853,the specificity was 0.827,and the maximum area under the ROC curve detected jointly was 0.854,indicating that the prediction ability of the model was strong.Conclusion:Serum KL-6 levels in RA-ILD patients are significantly increased.KL-6 can be used as a serological index for early detection of ILD,and combined with lung function detection can detect ILD earlier.Early diagnosis is of great significance for treatment and prognosis.