In this paper, the formula that shows the divergency field of the vertical crustal deformation is deduced from Fourier series, and the data of the precise levelling for more than 30 years in North China were calculated. We draw a map of equal value of the divergency for each period and analyzed the relation between the earthquake activity and the divergency field in this area. The conclusion is as follows:(1) It is found by couples for the positive source region and the negative source region in the divergency map. The high density divergency field distributes between positive source region and negative source region, and the naught divergency field is also located among the positive source region and the negative source region. (2) It is loomed unanimously in distributing for the high density divergency belt and the structure fissure belt in North China, and most of them are unanimous in strike. (3) It is shown from the distribution of the interval formula among the positive source region and the negative source region that the divergency map moves from South to North and from East to west with the elapes of time.(4) The naught of divergency region of vertical crustal deformation field is a certain of the positive region of vertical crustal deformation field. The source region is a short-lived phenomenon, which are the scattered and the observed, and then it can keep the moving state for the inherence of crust. The short -lived phenomenon prefigUre a new pattern of crustal movement and the earthquake preparation would be finished. When the positive sourve region and the negative source region is occuring alternately, it is the normal state, but when the source- free region is occuring, it is perhaps an anomalous phenomenon.