Regular stress detection for the ferromagnetic components in the industrial field can ensure the safety of industrial equipment. This paper proposes a method of steel stress measurement based on magnetoelastic effects under weak alternating current (AC) induction magnetic field. Firstly, the magneticstress relationship of steel plates under weak AC magnetization condition is studied through finite element simulations and the position of the measuring point is optimized. Then the stress measurement experiment for different thermomagnetic treated steel plates is carried out under weak AC magnetization condition. Results demonstrate that the normal weak AC induction magnetic field near the steel plate surface under different frequencies has noticeable stresssensitive characteristics, when the elastic stress varies from 0 MPa to 167 MPa, the normal weak AC magnetic field amplitude on the surface of the steel plate has an approximately linear monotonic relationship with the stress, demagnetization and heat treatment can effectively improve the consistency of the stressmagnetic relationship of the same size steel plate, the weak AC magnetization condition has noncontact, good repeatability and ability of stress measurement to resist background magnetic interference.