The author comprehensively reviewed the mutual energy theory of electromagnetic field, including three axioms: (1) the law of conservation of electromagnetic energy, (2) the law that radiation does not overflow the universe, (3) the principle of mutual energy and self energy principle; the mutual energy theorem, mutual energy flow theorem, advanced wave existence theorem. According to the theory of mutual energy, electromagnetic radiation is an interaction between source and sink. The source is a primary coil of the transformer, transmitting antenna and the emitter charge. The sink is the secondary coil of the transformer, receiving antenna and absorbing body charge. The source emits retarded wave and the sink emits advanced wave. Electromagnetic radiation phenomena must include a transmitting antenna and a receiving antenna. At this time, the transmitting antenna is equivalent to the primary coil of the transformer, and the receiving antenna is equivalent to the secondary coil of the transformer. Essentially, an antenna system including a transmitting antenna and a receiving antenna is no different from a transformer system including a primary coil and a secondary coil. They all satisfy the same mutual energy theory. That is, retarded wave and advanced wave are synchronized and generate the mutual energy flow. Mutual energy flow is photons. The wave, including the retarded wave and the advanced wave, must collapse in reverse. The reverse collapse satisfies the Maxwell equation of time reversal. The retarded wave and time reversal wave can be replaced by a reactive power wave. The mutual energy flow and reactive power wave together describe the wave collapse phenomenon. The important conclusion of this theory is that the energy of an electromagnetic wave is transferred by mutual energy flow, not by self energy flow. A light source cannot produce radiation without the help of an environmental absorber. Photons are mutual energy flows. The author finds that Maxwell's equation is not automatically suitable for the theory of electromagnetic mutual energy, so it must be modified. This correction includes adding a time reversal wave, but considering that reactive power waves can also play the role of time reversal wave, the author thinks that reactive power waves can be used to replace time reversal waves in this correction. In this paper, the method of mutual energy theory is applied to two planar current transformer systems and two dipole antenna systems. These two examples verify the correctness of mutual energy theory.