In computerized tomography test, the position of recording point after data inversion is determined by the position of transmitting point and receiving point between the two probes. In order to find out the position of recording points, we carried out experiment on electro-magnetic probe shielding by steel pipes. The experiment show that the energy concentration area between the two probes is parallelogram, hence it is more reasonable to inverse parallelogram area with four electro-magnetic wave rays rather than one ray path. On this basis, we propose to obtain the four single inversion result from each ray path and average them as the final result. This method was applied to the data processing of karst exploration for Wuhan underground. Through comparison of inversion result, this method is verified to be more precise than single-path inversion in the environment of the same inversion software.