The magnetic characteristic of magnetic steel sheets that are used for stator core of motors changes with stress. This change of magnetic characteristic affects the characteristic of the motors. For example, iron loss increases because of stress that acts on the stator core inserted in a frame by shrink fit. In this paper, the authors focus on iron loss calculation. Calculation methods by considering stress distribution are proposed in order to carry out coupled stress and electromagnetic field analysis. The proposed methods are as follows: (1) considering von-Mises stress, (2) considering scalar value of principal stress, and (3) considering both principal stress and direction of magnetic flux density. The calculated results are compared with an examination result of the prototype PM motor in order to verify the validity of the methods. As a result, the method that considers principal stress and direction of magnetic flux density is the most precise among the three ones.