Through detailed derivation, graph presentation and discussion of the ratio relationship between the amplitude of the reflected wave and that of the incident wave, this article gives the detailed distribution map of phase difference between the reflected light and the incident light in the refractive index-incident angle space. At the same time, various conditions for the occurrence of half-wave loss are specified, including the half-wave loss of the reflected light when the light is emitted from the optically denser medium to the optically thinner medium. Here we show that when the light beam is shot from the optically denser medium to the optically thinner medium, the reflected wave may also occur half-wave loss; when the light beam is shot from the optically thinner medium to the optically denser medium, the reflected wave does not necessarily occur a half-wave loss. Our work clarifies and supplements some unclear conclusions in existing textbooks.