Magnetie Barkhausen noise is sensitive to stress, which is an in-situ non-destructive stress measurement technology withconvenient operation, high detection sensitivity and good repeatability. It has broad application prospect in residlual stress measurement,stress concentration zone evaluation of parts and bearing stress evaluation of struetures. The measurement of the maximum prineipal stressand its diretion during the measurement of the plane stress on the surface of ferromagnetic materials in engineering is an urgent problemto he solved. Proposes a plane stress measurement method based on the cireumferential magnetic Barkhausen noise distribution, andestablishes the solution of the plane stress tensor. The model realizes the demodulation of normal stress and shear stress in any direetionof the measuring point. Experiments have verified the effectiveness of this method. Measurement resulis show that when the principalstress is greater than 50 MPa, the measured maximum prineipal stress direction deviation is 10°, the maximum normal stress deviation is5 MPa and the maximum shear stress deviation is 6 MPa, which has high measurement accuracy