A stress element analysis method is proposed for calculating the stress field and birefringence at the center of fiber core with any shape of fiber stress region. With the help of solid mechanics module in COMSOL Multiphysics software, stress field distribution and birefringence at the center of optical fiber core with the different shapes such as rectangle, square, triangle, circular stress element are studied. The results show that the stress field and birefringence at stress-induced optical fiber core are independent of the shape and direction of stress elements if the area of stress elements is the same and the stress element is small enough. They are only related with the distance between the fiber core and the center of the stress element. When the stress element is close to the core, this relationship between birefringence and distance approaches inverse square. The correctness and effectiveness of stress element analysis method can be verified from the results. So with integration of the stress element, stress distribution and birefringence at fiber core with any shape of stress region can be obtained.