Based on the micro-rectangle magnetic film system, and the shape and the tilt of crystal easy axis introduced into the Stoner-Wohlfarth model, it was found that the expansion of astroid was caused by the size dwindlement of the sample, while the defects in shape and the tilt of crystal easy axis would both result in the formation of asymmetrical astroid.These results illuminated that, in micron order magnetic film systems such as magnetic random access memory, the shape and the tilt of crystal easy axis are important for determining the switch field of the film.