Using CMOSOL Multiphysics software, the near field effection was analyzed, which of pole-pole potential distribution in the three layer model. The potential of AM observation system was used to design different AB corrent electrode spacing, and distance of MN electric potential, WDJD-4 field test was adopted. Numerical simulation shows that the corrent electrode spacing greater influence on the two opposite the point source field, but the distortion at infinite distance within a certain range can be corrected. Field electrical sounding show that: small corrent electrode distance of AB cases, pole-pole sounding curve can not correctly reflect the electrical distribution of dielectric. Infinite distance RBN potential observation system makes the sounding curves deviate from the normal sounding curve, and even cause ambiguity negative resistivity inflection point. By the traditional electric field theoretical analysis, the apparent resistivity observation device using different formulas for calculating the correction formula of diode device is pushed to the near field under the influence of non infinite electrode. Sounding data correction error analysis shows that, in the infinite distance satisfies 1.5RAO≤ RBO≤ 5RAO , the correction error is less than 5%, can use the infinite electrode distance is increased by three times, and successfully applied to practical detection of underground working face.