Based on reference[1] and the dislocation theory and corresponding gravity change in the layered media offered by previous papers, authors modified two equations presented by reference[1] and studied the relation between dislocating gravity variations and the rectangular planes with different sizes, buried depths, dislocating directions and dislocating magnitudes by numerical simulating method. The dislocating conditions and gravitational anomaly of the Tangshan (M 7.8) and Gonghe (M 7.0) earthquakes were also simulated for several points in this paper to probe the complexity of the space and intensity distributions of the earthquake precursor field. The results show that the gravity change caused by dislocating is very complicated in space and intensity distributions, which is the combined result of deformation and stress variation due to dislocating effect, both negative and positive gravity variations can appear in earthquake effect area. The dislocating plane conditions above mentioned have strong influence on gravitational space and intensity distributions.The simulating results suggest that if one wants to analyze the gravity anomaly caused by an earthquake, one should consider the concrete mechanism of the event. An enlightenment for understanding the complexity of other geophysical precursors of earthquakes is provided in this paper.