There actually does not exist the plane electromagnetic wave described by sutra theory that electric field and magnetic field are in phase everywhere. The solut ion of Maxwell equations depends on the original value of electromagnetic field or boundary conditions. According to different fixed-solution conditions, the p lane electromagnetic modes obtained are different. The results indicate that the plane electromagnetic wave is a transverse wave; at different positions, the a mplitudes of periodically changing magnetic field blazed by periodically changin g electric field are different, so are the amplitudes of periodically changing electric field blazed by periodically changing magnetic field. The phase differe nce between electric field and magnetic field is different too.