Objective To construct a risk assessment scale for postoperative delirium(POD)in elderly patients undergoing hip and knee joint replacement and evaluate the effect.Methods A total of 474 elderly patients undergoing hip and knee arthroplasty from March 2021 to May 2022 were collected as the training set,and a total of 153 the homogeneous patients from January 2022 to May 2022 were collected as the validation set.The patients were divided into two groups based on whether or not POD occurred:non-POD group and POD group.Risk factors of POD in the training set were analyzed by univariate analysis and multifactorial logistic regression.The consistency of the model was evaluated by Homser-Lemeshow goodness of fit test.The postoperative delirium risk assessment scale was established after the selected variables as-signed value according to OR value,and the predictive efficacy of the scale was evaluated by receiver oper-ating characteristic(ROC)curve.The patients in the training set and the validation set were divided into two groups according to the cut-off value:high-risk and low-risk.The incidence rate of POD with different risk stratification was calculated and the applicability of the risk assessment scale was evaluated.Results Fifty-eight patients(12.2%)with POD in the training set,and nineteen patients(12.4%)with POD in the validation set.Multifactor logistic regression showed that age≥85 years,ASA physical status Ⅲ or Ⅳ,the mini-mental state examination(MMSE)score≤24 points,preoperative sleep disorder,comorbid neu-rological disorders,use of general anesthesia,and non-use of dexmedetomidine were independent risk factors of POD.The POD risk assessment scale was then published based the seven risk factors.The ROC curve showed that the area under the curve(AUC)for this scale to predict the risk of POD was 0.956(95%CI 0.937-0.975),and the risk stratification was performed with a cut-off value of 44.5 points,which divided the patients into low-risk and high-risk.Compared with low-risk,the incidence rate of POD in high-risk patients group was significantly increased(P＜0.001).Conclusion A risk assessment scale based on the seven risk factors:age≥85 years,ASA physical status Ⅲ or Ⅳ,MMSE score≤24 points,preoperative sleep disorder,combined neurological disease,use of general anesthetic modality,and non-use of dexmedetomidine,can effectively identify elderly patients undergoing hip and knee replacement who are at high risk of developing POD.