Abstract: It is analysed the mechanism of ground fissure in Heibei plain. From the Fig of Normalized Z index time series of rainy season in North China, one can get that the rain is corresponding earth fissure. It is founded that ground fissure is closely contacted with the change of groundwater. When the connection rigidity reduces, the structure loses its steadily. These changes occur and complete in instantaneous, and there is always following the appearance of earth fissure.