Objective To investigate the predictive value of the mini?fluid challenge test in elderly orthopedic patients for post?spinal anesthesia hypotension. Methods Seventy?two elderly patients who underwent elective hip or knee replacement surgery were rigorously screened according to predefined inclusion and exclusion criteria. All patients were scheduled for subarachnoid block anesthesia. Subjects were grouped based on changes in blood pressure within 15 minutes of assuming a supine position following single?shot lumbar anesthesia. According to previously established definitions of hypotension， they were categorized into either the hypotension group （H group） or the normal blood pressure group （N group）. Prior to spinal anesthesia， a mini?fluid challenge test was conducted using noninvasive cardiac output monitoring to measure the change in stroke volume index （ΔSVI）， and baseline circulatory data were recorded. Multivariate logistic regression analysis was employed to identify factors influencing outcomes in elderly patients undergoing orthopedic joint replacement surgery. Receiver operating characteristic （ROC） curves for ΔSVI were constructed， and the area under the curve （AUC） was calculated to evaluate its predictive performance. Results After spinal anesthesia， 29 patients （40.27%） experienced hypotension. Compared with Group N， patients in Group H who experienced hypotension within 15 minutes while in a supine position were significantly older， had a higher proportion of ASA grade III， and a higher prevalence of hypertension （P < 0.05）. The analysis results indicated that ΔSVI was an independent influencing factor for post?lumbar anesthesia hypotension in elderly patients. ΔSVI demonstrated a sensitivity of 82.8% and a specificity of 81.4% in predicting post?spinal anesthesia hypotension （PSAH） at a cut?off value of 0.805 or greater. There was a moderate positive linear correlation between the maximum decrease in systolic blood pressure （SBP） and ΔSVI （r = 0.562， P < 0.01）. Conclusion The mini?fluid challenge test is an effective method for predicting hypotension in elderly orthopedic patients following spinal anesthesia.