Objective To establish and verify the method for detecting human antithrombin Ⅲ(AT-Ⅲ activity by automatic coagulation analyzer. Methods According to the operation manual ofautomatic coagulation analyzer, the AT-Ⅲ activity was detected, and the linearity and detection range, precision and accuracy of the method were verified. Results Automatic coagulation analyzer detectdAT-Ⅲ activity stably and automatically ran the standard curves with coefficients of determination all>0.980, the standard curve of the calibrator was 0. 12-1. 23 IU/ml, the titer recovery rate range of thehigh, middle, low value calibrator and quantitative lower limit dilution samples were 80%-120%.therelative standard deviations (RSDs) of the high, middle and low value titer recovery rates were<15%,and the RSD of quantitative lower limit dilution sample titer recovery rate was <20%, inter-batch RSDs for the test products were <5%, and the intra-batch RSDs were <10%. The average RSDs of 3 batches of AT Ⅲ products and intermediates tested 3 times were all <5%. Conclusion The method of automatic coagulation analyzer for detecting AT-Ⅲ activity has good linearity, test range, accuracy and precision, which can be used for the detection of AT-Ⅲ activity in the production process.