The loss of phase period of VLFradiowaye propagation during solar flares is discussed based on experimental data. Furthermore, the mechanism of loss of phase period is explained utilizing a theory of antipodal propagation. Loss of phase period is an improtant phenomenon of radiowave propagation, especially, the propagation of LFand VLFradiowaves. The phenomenon discussed above is seldomly seen in past references. Therefore, discussion on the problem is of special significant.