In order to solve the influence of antenna length on the numerical simulation of borehole ground penetrating radar, this paper studies the mutual conversion of current to voltage in the antenna through theoretical derivation and numerical calculation. For the transmitted signal, we first obtain the current distribution in the antenna according to the convolution of the excitation voltage and the electric field in the calculated area.For the electric field and convolution at the receiving antenna of the received signal, the infinitesimal current intensity of the antenna is obtained, and then the total current of the antenna is obtained by integrating the length of the antenna. The voltage received at that time can be obtained by multiplying the load resistance of the receiving antenna. The results of theoretical calculation and numerical simulation show that the received signal waveform is basically the same as the transmitted signal waveform. It is concluded that the expression of the received and received signals based on the proposed algorithm is accurate under the premise of considering the antenna length.