Objective:To explore the threshold and diagnostic value of Chinese version of the Chelsea Physical Function Assessment Tool (CPAx-Chi) for ICU acquired weakness(ICU-AW).Methods:To learn the details and precautions of the CPAx-Chi scale, and then two researchers used the CPAx-Chi scale and MRC-Score scale to independently evaluate 200 patients who come from a comprehensive ICU in a top first-class hospital in Gansu Province simultaneously. The best cut-off point and value of the CPAx-Chi scale in the diagnosis of ICU-AW were determined by calculating the Receiver Operating Characteristic (ROC) curve, the Youden index(YI) and the consistency test that are all based on the MRC-Score≤48.Results:The ROC Area Under Curve(AUC) of the CPAx-Chi scale diagnosis ICU-AW which based on the MRC-Score≤48 were as follows: ROC AUC of group A was 0.899 (95% CI 0.862-1.025); ROC AUC of group B was 0.874 (95% CI 0.824-0.925). When the best cut-off point of CPAx-Chi scale for diagnosis ICU-AW was 31.5, the maximum YI=0.643, the sensitivity was 87%, and the specificity was 77% in group A; and the maximum YI= 0.62, the sensitivity was 75%, and the specificity was 87% in group B. Meanwhile, when the best cut-off point of CPAx-Chi scale for diagnosis ICU-AW was 30.5, the maximum YI=0.62, the sensitivity was 79%, and the specificity was 83% in group B. Taking the CPAx -Chi≤31 as the best cut-off point, the score differences in ICU-AW group and the non-ICU-AW group were not detected, A group ( F value was 4.53, P=0.035) or B group ( F value was 6.51, P=0.011). The consistency of CPAx -Chi≤31 and MRC-Score≤48 in the diagnosis of ICU-AW was high, and the Kappa=0.845 ( P=0.02) in the group A; the Kappa=0.839( P=0.04) in the group B, and the group differences were detected. Conclusions:CPAx-Chi≤31 is the best cut-off point for diagnosing ICU-AW, and has good sensitivity and specificity. CPAx-Chi scale can be popularized and applied in the critical care medicine in China.