Three dimensional geophysical models were abstracted and established according to characteristics of oil and gas reservoir. Then direct current fields for different models were simulated with finite element software (finite element program generator) by hole-to-surface resistivity method. Numerical solution was compared with analytical one for the homogeneity earth model. And a new parameter of deviation rate was proposed by analyzing different plot curves. The results show that the relative error of solution for homogeneity earth model may attain to 0.043%. And deviation rate decreases from 18% to 1% and its anomaly range becomes wide gradually when the depth of oil and gas reservoir increases from 200 to 1 500 m. If resistivity ratio of oil and gas reservoir to sur- rounding rock decreases from 100 to 10 for the resistive oil and gas reservoir, the amplitude attenuation of deviation rate nearly reaches 8%. When there exists stratum above oil and gas reservoir, and influence of resistive stratum may be eliminated or weakened and anomaly of oil and gas reservoir can be strengthened.