The novel soft magnetic materials and magnetic core structure used in planar transformer have been studied. The frequency, electrical and structure feature of the planar transformer with matrix structure was described. Then the novel magnetic materials used in the planar transformer were discussed, which were very different from ferrite block. The silicon steel strip was first represented, the magnetic characteristic of which was related to its geometric dimension, working frequency and the component. The microcrystallite alloy and amorphous alloy magnetic materials were then indicated, including iron-base nanocrystal and cobalt-base amorphous alloy. The magnetic materials of the above amorphous alloy and microcrystallite alloy were compared respectively. These soft magnetic materials could be used as the magnetic core in planar transformer, and the magnetic core could be composed of thin strip and line. The structure of magnetic core was flexible, which could benefit the planar transformer to reduce its volume. The development and trendy of novel magnetic materials and magnetic core in planar transformer were analyzed and discussed in this paper.