Abstract: With the increase of iron core size in super large-capacity machines and transformers, the magnetostriction in electrical steel sheet aggravates vibration and noise of iron core. In order to develop the magnetostriction property of electrical steel sheet under alternating magnetization conditions, a conventional magnetostriction tester for a single electrical steel sheet was improved. A "three-axial laser" method was proposed to measure vector magnetostriction property of electrical steel sheet along different magnetization directions at the angles of 0o to 90 o to rolling direction and the relationship between principal strain of magnetostriction and magnetization direction and strength was studied. A vector model describing the relationship between principal strain vector of magnetostriction and magnetic flux density vector was proposed and the two-dimensional interpolating surface was built. By combining the model and finite element computation, the magnetostriction phenomenon in the stator core of a permanent magnet synchronous motor was analyzed. The studies show that the principal strain direction deviates from magnetization direction, and the measurement and simulation method proposed can be effectively used to develop the vector magnetostriction effect of motor core.