We experimentally and theoretically studied interpretation of the waveform signal which was obtained by the fiber-optic probe method during Ho:YAG laser ablation. We monitored behavior of the ablation bubble which occurs at the fiber tip during the ablation by means of developed fiber-optic probe method as well as time-resolved photography to investigate the information which involves the waveform signal. We used water and agar as model materials for different purposes. We determined that the waveform signal from the fiber-optic probe method is mainly attributed to the reflection of the boundary between the water-vapor bubble and surrounding material/tissue. We also found that the intensive shockwave which is induced may be monitored by our method.