On the basis of the hard inclusion earthquake preparation model (HEPM for short) and referring intraplate earthquake preparation characteristics and geologic structure feature of North China,model of crustal structure of four layers with a hard inclusion,a soft inclusion and a vertical fault is constructed. Dynamic simulation on the space time distribution of deformation and stress fields near surface for the model is carried out. The results show that at beginning of earthquake preparation, deformation near surface of the hard inclusion in the model is relatively stable, a deformation gap is showed. During the medium short term period before earthquake, the deformation increased swiftly. Meanwhile, the average stress in the region strengthened obviously,which is the inner mechanism for migration of precursory anomalies with regularity from outer area to epicenter area of strong earthquake.