Borehole radar is a well geophysical method for obtaining the high-resolution information of deep underground environment. According to the common point unfavorable geo-bodies in borehole radar exploration

such as cavities

karst caves and buried objects

etc.

the forward simulation of response of the tool to point unfavorable geo-bodies of different surrounding rock and filling condition is investigated with finite difference time domain (FDTD) method. The influence of surrounding rock and filling condition on response characteristics of borehole radar is analyzed. The results indicate that the relative value of dielectric constant of surrounding rock and filling substance affects the contrast of radar reflection profile

and when the relative value of dielectric constant increasing

it is easier to ascertain the subsurface media distribution. While high-conductivity surrounding rock can attenuate most of radar signal

it is almost impossible to detect the cavities with single borehole reflection method. According to the different borehole radar cross-sectiorn and its response characteristics

the filling condition in the cavities can be qualitatively distinguished.