Abstract: Tension-torsion biaxial low cycle fatigue tests have been carried ou t on thin-walled tubes with circular holes made from 40 Cr steel. Stress and strain distribution near the circular hole has been analysed with elastic-plastic finite element method. Previous multiaxial fatigue criteria were re-examined. Based on the experimental results and the analysis of thin-walled tuble tension-torsion biaxial fatigue, a new maltiaxial fatigue criterion has been proposed,which predicts both fatigue initiation life and cracking site quite satisfactorily.